Originally Posted by lucid
Since wwdj didn't mention anything about pedal feel, my money would be on ABS operation rather than the brake boost levels in this particular scenario where braking distances vary in the absence of difference in pedal feel. If brake boost was to drop off, you should have a solid pedal but can still brake with you stand on it. In other words, there should be a direct and very observable difference in pedal feel.
If ABS is not working properly in certain conditions (which could be an issue with the modified bias of an aftermarket system), you might not always feel something significantly different in pedal feel, but can experience significant differences in stopping power/distance. One can usually observe what I mean when trying to threshold brake at a bumpy braking zone vs. a smooth one on the same day at the same track. (Of course, braking on a bumpy section complicates traction as well, which also factors into ABS operation).
Anyway, I am speculating and there are many potential causes that might explain the inconsistency.
I don't know if I'm fast, but I've been having this issue for a while now (Brembo BBK). Would pre-tapping the brake pedal before braking help towards this issue?