On wall, you can f4 after his most damaging 3xb12f1 juggles, so why limit yourself in terms of damage? If you know that after Lift you won't connect b1, you can use 31, 31 f4 to keep them in the corner.
In that case of far Lift, jump punch b12f1 b12f1 f4 it is much easier to conect Lift dash f+2 3,1 f+4; you sacrifice only 2% of damage and get the same reset situation.
After jiP u4_f4 isn't really a reliable 50/50, everyone can easily fuzzy guard this; Ermac's u4 is almost the same speed as Mileena's and I don't think anyone has problems with her 50/50 (b3/u4) which is even better, because leads to full combo & is not punishable (u4 being +9 on block, b3 only -3 - comparing it to Ermac's analogic options makes him sad). It is good to surprise the opponent or crush low moves, though.
Just some random setup: when you get the f+4 reset in the corner, you have guaranteed uninterruptable 31 opportunity, (there's no pushback and 3 is in range; midscreen it'll whiff because of f+4 moving the opp away), you can go for 312 and if it hits (or simply when you hit 312 in the corner) instead of trying a safejump, b2 charge etc. you can go for f+2 (which will be also uninterruptable). If it hits, you can easily hitconfirm it into d+1~TKS and juggle and if it's blocked you have frame advantage, so immiediately do d1 - you will always catch the opponent if he tries to jump out and confirm it into second d1 cancelled into TKS&combo.