the pmc tanking shots probably has to do with the health multiplier that AKI has. You can change that in FAIT. That or he had a helmet and you had bad rounds.
As far as you dying quickly first off level 4 armor is pretty crap and even with level 6 armor you can still get two tapped in the chest by high end rounds in EFT. None of this is really FAITs fault.
i removed the mod and have no issues now. not getting 2 tap instantly and being able to actually have a fight instead of dying to a pmc thats suppose to miss their first shots and then get better. they aim bot their first shots, and when i kill one several in surrounding area will just come straight to me. like on reserve i killed a pmc behind one of the pawn buildings and all other pmcs in surrounding buildings just made their way right to me as i was looting. but like i said no issues now with the mod removed. the mod didnt feel good. i was getting 2 tapped with crap rounds from the pmc.