[Ejidoth]

While that's probably where the original conversion came from, it's used in several places, the corruption rules being one of them. Notably, for comparison, Impulse Buys outright has a 'buy a non-regenerating 25 FP reserve for 1 character point' option.

Basically, when converting temporary FP costs to permanent costs, 25 FP = 1 character point appears to be the accepted standard.