The IF change is welcome and definitely adds an interesting mechanic. However, I notice that when wearing medium armor, you don't see any wpf advantage from IF until you exceed 3-4 points in the skill. This is unfortunate, since most people are now lvl 37 and that level doesn't allow "complete" builds, so you end up with "leftover" points. However, IF isn't a great option for leftover points, since you don't get the wpf benefit unless you are nearly maxing it.
I wish the wpf benefit could be linear with IF skill, instead of loaded to the last few points as you max IF. This would encourage greater build variety, as the IF skill is now very "all or nothing". The strength component of the wpf penalty reduction formula is nearly insignificant; I'd rather see it be a simple linear function of IF.