UTL_MATCH.JARO_WINKLER_SIMILARITY - how can I set the prefix scale?

Question

I'm using UTL_MATCH's Jaro Winkler similarity function and it seems to be performing well. However, I would like to adjust the prefix scale according to the situation. Is this possible? Is it possible to see what the default prefix scale is? I could not find any documentation on this, but it seems that in order to be a J-W distance, it must use a prefix scale.