Have you tried a STF with 20 WPF? I'll make one with a guess at a typical build after patch if you want and we can duel lol
It seems pretty tight to have only give 20 "free" WPF, without doing any testing if I would have picked a number I would have given 50 (as that's what you can currently get at 1 WPP per WPF).
I wonder how much/what testing Tydeus etc did before choosing this as a base value.