Richard,

I really think this is a great question you have posed. My answer got longer than I anticipated so in summary I have 3 possible solutions based on what you asked. If I had to rank my preference I would do:

1. Multiple Child Tables
2. Single "Extension" table
3. EVA table

EVA Approach

My initial response was the EVA design method, however I don't think that is the solution you want to go with. My concern is when it comes to trying to SELECT data out of the EVA table. You would need to do 16 LEFT OUTER JOIN's each time you wanted to get all 16 OPTIONS. Potentially something like this:

DECLARE @Option1Default Decimal(10,5), --Or Whatever the appropriate datatype is
@Option2Default Decimal(10,5),
@Option3Default Decimal(10,5),
@Option4Default Decimal(10,5),
@Option5Default Decimal(10,5),
@Option6Default Decimal(10,5),
@Option7Default Decimal(10,5),
@Option8Default Decimal(10,5),
@Option9Default Decimal(10,5),
@Option10Default Decimal(10,5),
@Option11Default Decimal(10,5),
@Option12Default Decimal(10,5),
@Option13Default Decimal(10,5),
@Option14Default Decimal(10,5),
@Option15Default Decimal(10,5),
@Option16Default Decimal(10,5)

SET @Option1Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 1')
SET @Option2Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 2')
SET @Option3Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 3')
SET @Option4Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 4')
SET @Option5Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 5')
SET @Option6Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 6')
SET @Option7Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 7')
SET @Option8Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 8')
SET @Option9Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 9')
SET @Option10Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 10')
SET @Option11Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 11')
SET @Option12Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 12')
SET @Option13Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 13')
SET @Option14Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 14')
SET @Option15Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 15')
SET @Option16Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 16')

SELECT PYDC.Oid,
CASE
    WHEN PYDCOC1.CustomValue IS NULL THEN @Option1Default
    ELSE PYDCOC1.CustomValue
    END AS Option1Value,
CASE
    WHEN PYDCOC2.CustomValue IS NULL THEN @Option2Default
    ELSE PYDCOC2.CustomValue
    END AS Option2Value,
CASE
    WHEN PYDCOC3.CustomValue IS NULL THEN @Option3Default
    ELSE PYDCOC3.CustomValue
    END AS Option3Value,
CASE
    WHEN PYDCOC4.CustomValue IS NULL THEN @Option4Default
    ELSE PYDCOC4.CustomValue
    END AS Option4Value,
CASE
    WHEN PYDCOC5.CustomValue IS NULL THEN @Option5Default
    ELSE PYDCOC5.CustomValue
    END AS Option5Value,
CASE
    WHEN PYDCOC6.CustomValue IS NULL THEN @Option6Default
    ELSE PYDCOC6.CustomValue
    END AS Option6Value,
CASE
    WHEN PYDCOC7.CustomValue IS NULL THEN @Option7Default
    ELSE PYDCOC7.CustomValue
    END AS Option7Value,
CASE
    WHEN PYDCOC8.CustomValue IS NULL THEN @Option8Default
    ELSE PYDCOC8.CustomValue
    END AS Option8Value,
CASE
    WHEN PYDCOC9.CustomValue IS NULL THEN @Option9Default
    ELSE PYDCOC9.CustomValue
    END AS Option9Value,
CASE
    WHEN PYDCOC10.CustomValue IS NULL THEN @Option10Default
    ELSE PYDCOC10.CustomValue
    END AS Option10Value,
CASE
    WHEN PYDCOC11.CustomValue IS NULL THEN @Option11Default
    ELSE PYDCOC11.CustomValue
    END AS Option11Value,
CASE
    WHEN PYDCOC12.CustomValue IS NULL THEN @Option12Default
    ELSE PYDCOC12.CustomValue
    END AS Option12Value,
CASE
    WHEN PYDCOC13.CustomValue IS NULL THEN @Option13Default
    ELSE PYDCOC13.CustomValue
    END AS Option13Value,
CASE
    WHEN PYDCOC14.CustomValue IS NULL THEN @Option14Default
    ELSE PYDCOC14.CustomValue
    END AS Option14Value,
CASE
    WHEN PYDCOC15.CustomValue IS NULL THEN @Option15Default
    ELSE PYDCOC15.CustomValue
    END AS Option15Value,
CASE
    WHEN PYDCOC16.CustomValue IS NULL THEN @Option16Default
    ELSE PYDCOC16.CustomValue
    END AS Option16Value
FROM ProductYearDistrictCrop PYDC   
    LEFT OUTER JOIN ProductYearDistrictCropOptionChoices PYDCOC1
        ON PYDC.Oid = PYDCOC1.Oid --assuming that is the FK on ProductYearDistrictCropOptionChoices that references ProductYearDistrictCrop.Oid
        AND PYDCOC1.OptionID = 1
    LEFT OUTER JOIN ProductYearDistrictCropOptionChoices PYDCOC2
        ON PYDC.Oid = PYDCOC2.Oid 
        AND PYDCOC2.OptionID = 2
    LEFT OUTER JOIN ProductYearDistrictCropOptionChoices PYDCOC3
        ON PYDC.Oid = PYDCOC3.Oid 
        AND PYDCOC3.OptionID = 3
    LEFT OUTER JOIN ProductYearDistrictCropOptionChoices PYDCOC4
        ON PYDC.Oid = PYDCOC4.Oid 
        AND PYDCOC4.OptionID = 4
    LEFT OUTER JOIN ProductYearDistrictCropOptionChoices PYDCOC5
        ON PYDC.Oid = PYDCOC5.Oid 
        AND PYDCOC5.OptionID = 5
    LEFT OUTER JOIN ProductYearDistrictCropOptionChoices PYDCOC6
        ON PYDC.Oid = PYDCOC6.Oid 
        AND PYDCOC6.OptionID = 6
    LEFT OUTER JOIN ProductYearDistrictCropOptionChoices PYDCOC7
        ON PYDC.Oid = PYDCOC7.Oid 
        AND PYDCOC7.OptionID = 7
    LEFT OUTER JOIN ProductYearDistrictCropOptionChoices PYDCOC8
        ON PYDC.Oid = PYDCOC8.Oid 
        AND PYDCOC8.OptionID = 8
    LEFT OUTER JOIN ProductYearDistrictCropOptionChoices PYDCOC9
        ON PYDC.Oid = PYDCOC9.Oid 
        AND PYDCOC9.OptionID = 9
    LEFT OUTER JOIN ProductYearDistrictCropOptionChoices PYDCOC10
        ON PYDC.Oid = PYDCOC10.Oid 
        AND PYDCOC10.OptionID = 10
    LEFT OUTER JOIN ProductYearDistrictCropOptionChoices PYDCOC11
        ON PYDC.Oid = PYDCOC11.Oid 
        AND PYDCOC11.OptionID = 11
    LEFT OUTER JOIN ProductYearDistrictCropOptionChoices PYDCOC12
        ON PYDC.Oid = PYDCOC12.Oid 
        AND PYDCOC12.OptionID = 12
    LEFT OUTER JOIN ProductYearDistrictCropOptionChoices PYDCOC13
        ON PYDC.Oid = PYDCOC13.Oid 
        AND PYDCOC13.OptionID = 13
    LEFT OUTER JOIN ProductYearDistrictCropOptionChoices PYDCOC14
        ON PYDC.Oid = PYDCOC14.Oid 
        AND PYDCOC14.OptionID = 14
    LEFT OUTER JOIN ProductYearDistrictCropOptionChoices PYDCOC15
        ON PYDC.Oid = PYDCOC15.Oid 
        AND PYDCOC15.OptionID = 15
    LEFT OUTER JOIN ProductYearDistrictCropOptionChoices PYDCOC16
        ON PYDC.Oid = PYDCOC16.Oid 
        AND PYDCOC16.OptionID = 16
--WHERE Condition(s)

What I am not overly fond of is the idea of having to make 16 JOINS to the same table. You just run into a high potential for locking on that table, particularly if this query is used a lot. Indexing can get you around a lot of it but you will still have a lot of hits to this table every time you need to read from it.

Extension Table Approach

When It Comes To The Additional Columns Approach most people's concern is that it isn't normalized out. I hear a comment one time about "Normalize until it hurts. De-Normalize until it works". (There is actually a DBA Stack Exchange topic which covered this idea about how far to go with Normalization). With all that in mind if this is going to be a highly utilized part of the database than this may be a candidate where taking a slightly de-normalized design, for performance reasons may be what you want to do.

I would not however recommend adding the columns onto your existing table. The wider the table is, the less data you can fit onto the same page which means that everything else using this table will take a performance degradation. One way around that is creating an "Extension" table which doesn't do anything but hold these values. You would simply JOIN to this one table to get all 16 options (whether they are always written, or the columns are NULLABLE and only hold have a value if it differs from the default). When an additional Option is added, you would just add a new column to this table.

This table, space-wise would be really inefficient. But we would be sacrificing that space, for SELECT query performance in both instances where ProductYearDistrictCrop is used without this new extension table and when ProductYearDistrictCrop is used in unison with it.

CREATE TABLE [dbo].[ProductYearDistrictCropOptions]
(
    [Oid] [BIGINT] NOT NULL,
    [Option1] [Decimal(10,5)] NULL, --Or Whatever the appropriate datatype is
    [Option2] [Decimal(10,5)] NULL, 
    [Option3] [Decimal(10,5)] NULL, 
    [Option4] [Decimal(10,5)] NULL, 
    [Option5] [Decimal(10,5)] NULL, 
    [Option6] [Decimal(10,5)] NULL, 
    [Option7] [Decimal(10,5)] NULL, 
    [Option8] [Decimal(10,5)] NULL, 
    [Option9] [Decimal(10,5)] NULL, 
    [Option10] [Decimal(10,5)] NULL, 
    [Option11] [Decimal(10,5)] NULL, 
    [Option12] [Decimal(10,5)] NULL, 
    [Option13] [Decimal(10,5)] NULL, 
    [Option14] [Decimal(10,5)] NULL, 
    [Option15] [Decimal(10,5)] NULL, 
    [Option16] [Decimal(10,5)] NULL, 
    
    CONSTRAINT [PK_ProductYearDistrictCropOptions] PRIMARY KEY CLUSTERED 
    (
        [Oid] ASC
    )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 90) ON [PRIMARY]
) ON [PRIMARY]

ALTER TABLE [dbo].[ProductYearDistrictCropOptions]  WITH CHECK ADD  CONSTRAINT [FK_ProductYearDistrictCropOptions_ProductYearDistrictCrop] FOREIGN KEY([Oid])
REFERENCES [dbo].[ProductYearDistrictCrop] ([Oid])
GO

ALTER TABLE [dbo].[ProductYearDistrictCropOptions] CHECK CONSTRAINT [FK_ProductYearDistrictCropOptions_ProductYearDistrictCrop]
GO

Multiple Child Table Approach

You can get around the poor space utilization with multiple child tables

I was reading an article the other day reference in a different DBA Stack Exchange Question on NULLS. This Article suggested that multiple child tables holding values can be used to designate this. Where each option has its own child table which holds this data. You would end up creating 16 version of something like:

CREATE TABLE [dbo].[ProductYearDistrictCropOption1Values]
(
    [Oid] [BIGINT] NOT NULL,
    [Value] [Decimal(10,5)] NOT NULL, --Or Whatever the appropriate datatype is
    
    CONSTRAINT [PK_ProductYearDistrictCropOption1Values] PRIMARY KEY CLUSTERED 
    (
        [Oid] ASC
    )WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, FILLFACTOR = 90) ON [PRIMARY]
) ON [PRIMARY]

ALTER TABLE [dbo].[ProductYearDistrictCropOption1Values]  WITH CHECK ADD  CONSTRAINT [FK_ProductYearDistrictCropOption1Values_ProductYearDistrictCrop] FOREIGN KEY([Oid])
REFERENCES [dbo].[ProductYearDistrictCrop] ([Oid])
GO

ALTER TABLE [dbo].[ProductYearDistrictCropOption1Values] CHECK CONSTRAINT [FK_ProductYearDistrictCropOption1Values_ProductYearDistrictCrop]

You would then reference everything by using something like

DECLARE @Option1Default Decimal(10,5), --Or Whatever the appropriate datatype is
@Option2Default Decimal(10,5),
@Option3Default Decimal(10,5),
@Option4Default Decimal(10,5),
@Option5Default Decimal(10,5),
@Option6Default Decimal(10,5),
@Option7Default Decimal(10,5),
@Option8Default Decimal(10,5),
@Option9Default Decimal(10,5),
@Option10Default Decimal(10,5),
@Option11Default Decimal(10,5),
@Option12Default Decimal(10,5),
@Option13Default Decimal(10,5),
@Option14Default Decimal(10,5),
@Option15Default Decimal(10,5),
@Option16Default Decimal(10,5)

SET @Option1Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 1')
SET @Option2Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 2')
SET @Option3Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 3')
SET @Option4Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 4')
SET @Option5Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 5')
SET @Option6Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 6')
SET @Option7Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 7')
SET @Option8Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 8')
SET @Option9Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 9')
SET @Option10Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 10')
SET @Option11Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 11')
SET @Option12Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 12')
SET @Option13Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 13')
SET @Option14Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 14')
SET @Option15Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 15')
SET @Option16Default = (SELECT SystemDefaultValue FROM Options WHERE [Description] = 'Option 16')

SELECT PYDC.Oid,
CASE
    WHEN PYDCOC1.[Value] IS NULL THEN @Option1Default
    ELSE PYDCOC1.[Value]
    END AS Option1Value,
CASE
    WHEN PYDCOC2.[Value] IS NULL THEN @Option2Default
    ELSE PYDCOC2.[Value]
    END AS Option2Value,
CASE
    WHEN PYDCOC3.[Value] IS NULL THEN @Option3Default
    ELSE PYDCOC3.[Value]
    END AS Option3Value,
CASE
    WHEN PYDCOC4.[Value] IS NULL THEN @Option4Default
    ELSE PYDCOC4.[Value]
    END AS Option4Value,
CASE
    WHEN PYDCOC5.[Value] IS NULL THEN @Option5Default
    ELSE PYDCOC5.[Value]
    END AS Option5Value,
CASE
    WHEN PYDCOC6.[Value] IS NULL THEN @Option6Default
    ELSE PYDCOC6.[Value]
    END AS Option6Value,
CASE
    WHEN PYDCOC7.[Value] IS NULL THEN @Option7Default
    ELSE PYDCOC7.[Value]
    END AS Option7Value,
CASE
    WHEN PYDCOC8.[Value] IS NULL THEN @Option8Default
    ELSE PYDCOC8.[Value]
    END AS Option8Value,
CASE
    WHEN PYDCOC9.[Value] IS NULL THEN @Option9Default
    ELSE PYDCOC9.[Value]
    END AS Option9Value,
CASE
    WHEN PYDCOC10.[Value] IS NULL THEN @Option10Default
    ELSE PYDCOC10.[Value]
    END AS Option10Value,
CASE
    WHEN PYDCOC11.[Value] IS NULL THEN @Option11Default
    ELSE PYDCOC11.[Value]
    END AS Option11Value,
CASE
    WHEN PYDCOC12.[Value] IS NULL THEN @Option12Default
    ELSE PYDCOC12.[Value]
    END AS Option12Value,
CASE
    WHEN PYDCOC13.[Value] IS NULL THEN @Option13Default
    ELSE PYDCOC13.[Value]
    END AS Option13Value,
CASE
    WHEN PYDCOC14.[Value] IS NULL THEN @Option14Default
    ELSE PYDCOC14.[Value]
    END AS Option14Value,
CASE
    WHEN PYDCOC15.[Value] IS NULL THEN @Option15Default
    ELSE PYDCOC15.[Value]
    END AS Option15Value,
CASE
    WHEN PYDCOC16.[Value] IS NULL THEN @Option16Default
    ELSE PYDCOC16.[Value]
    END AS Option16Value
FROM ProductYearDistrictCrop PYDC   
    LEFT OUTER JOIN ProductYearDistrictCropOption1Values PYDCOC1
        ON PYDC.Oid = PYDCOC1.Oid --assuming that is the FK on ProductYearDistrictCropOption1Values that references ProductYearDistrictCrop.Oid
    LEFT OUTER JOIN ProductYearDistrictCropOption2Values PYDCOC2
        ON PYDC.Oid = PYDCOC2.Oid 
    LEFT OUTER JOIN ProductYearDistrictCropOption3Values PYDCOC3
        ON PYDC.Oid = PYDCOC3.Oid 
    LEFT OUTER JOIN ProductYearDistrictCropOption4Values PYDCOC4
        ON PYDC.Oid = PYDCOC4.Oid 
    LEFT OUTER JOIN ProductYearDistrictCropOption5Values PYDCOC5
        ON PYDC.Oid = PYDCOC5.Oid 
    LEFT OUTER JOIN ProductYearDistrictCropOption6Values PYDCOC6
        ON PYDC.Oid = PYDCOC6.Oid 
    LEFT OUTER JOIN ProductYearDistrictCropOption7Values PYDCOC7
        ON PYDC.Oid = PYDCOC7.Oid 
    LEFT OUTER JOIN ProductYearDistrictCropOption8Values PYDCOC8
        ON PYDC.Oid = PYDCOC8.Oid 
    LEFT OUTER JOIN ProductYearDistrictCropOption9Values PYDCOC9
        ON PYDC.Oid = PYDCOC9.Oid 
    LEFT OUTER JOIN ProductYearDistrictCropOption10Values PYDCOC10
        ON PYDC.Oid = PYDCOC10.Oid 
    LEFT OUTER JOIN ProductYearDistrictCropOption11Values PYDCOC11
        ON PYDC.Oid = PYDCOC11.Oid 
    LEFT OUTER JOIN ProductYearDistrictCropOption12Values PYDCOC12
        ON PYDC.Oid = PYDCOC12.Oid 
    LEFT OUTER JOIN ProductYearDistrictCropOption13Values PYDCOC13
        ON PYDC.Oid = PYDCOC13.Oid 
    LEFT OUTER JOIN ProductYearDistrictCropOption14Values PYDCOC14
        ON PYDC.Oid = PYDCOC14.Oid 
    LEFT OUTER JOIN ProductYearDistrictCropOption15Values PYDCOC15
        ON PYDC.Oid = PYDCOC15.Oid 
    LEFT OUTER JOIN ProductYearDistrictCropOption16Values PYDCOC16
        ON PYDC.Oid = PYDCOC16.Oid 
--WHERE Condition(s)

This version is:

1. Normalized and prevents you from adding a bunch of extra columns making ProductYearDistrictCrop wider
2. Allows you to only insert values where that particular ProductYearDistrictCrop.Oid is different than the default. Which allows you to save a lot of space
3. Additional options only requires an additional table following the same format which is then supported with code updates in whatever functions/queries/stored procedures.

That is probably one of the harder ones to support when it comes to new options coming. It will also require the most amount of work in your initial development. But a VIEW can probably be used to get around most of that. However I think space and performance wise it will give you the best of both worlds, which should be the primary priority when it comes to a database, particularly if you are already in a 2 Million row world with this one table.