Hm, 25.50% of $25.00 is $6.38 (rounded from $6.375), suggesting you'd entered the 50% extra percentage as a multiplier figure of "0.50" rather than a percentage figure of "50.0"; however, it appears your affiliates' extra percentages are currently entered correctly as "50.0".
I've asked Development to make sure we're calculating the extra percentage correctly, but by any chance did you already change your extra percentage figures to fix this?