If you go back to the initial post:
I assume piggybacking at 100% is still better than the current systemCurrently a single two weapon fighting attack makes a physics detection check with your main hand, followed by a second detection check for your off hand (roughly 0.15 seconds after the first one). Instead of making multiple physics checks, all two weapon fighting attacks (weapons or unarmed) would now make a single check for your main hand attack, and would “piggyback” on that detection check and have a chance to proc (trigger) an off-hand attack based on the number of two weapon fighting feats (or related enhancements) you possess. Off-hand attacks would have a chance to proc on any main hand attack now, instead of being predetermined on certain attacks. Having more TWF feats increases the % chance of proccing an off-hand attack
edit: doh, got beaten to it.