Right now body armor in arma seems to be very inaccurate, because as far as i understand armor value from vest is used to multiply your "HP" of hitpoint which is complete nonsense. Recently we started to use mods that provide higher body armors like 6B5, 5.11 Tactec or 6B43 all of these are labeled as level 5
The problem starts when we want to use specific ammo let's say M995 AP based on Escape from Tarkov values. We have higher penetration value with lower body damage. In arma we have only the magical "Hit" parameter which is the only source for damage on players. we run 10 different tests with different values for:
typicalSpeed
caliber
airFriction
all of these have almost no impact on players. Now we run into balancing problems, if we want to make AP ammo somehow different from normal (M855) we need to modify this stupid "Hit" paramter which results in simply "better" ammo because overall it just does more damage it's not situational like in EFT, but simply better. So far we tried using attach to with attaching various objects for players, trying to use CfgArmorSimulations for body armor (it has no effect on body armor as far as we could see)
The best solution would be to add a new parameter which would be used as a multiplier to lower armor values of the vest. For sake of not breaking any mods keep default value as 1.0 for bullet_base, so mods can later get updated to use this method