It's interesting to hear what COMBATMED101 has to say.
If I were to summarise:
I don't want to get into the debate about how you will react in your mind and all that. But some obvious issues with this involve BALANCE.
Let's talk about balance.
If you're at ease, relaxed, any round will knock you down. A small shove will knock you down, so a bullet is definitely going to throw you off balance. This is due to narrow foot placement and high centre of gravity.
If you're leaning into your weapon, ready to fire, you've naturally got very high stability, as you're already braced to take the recoil of your weapon. This is due to wide foot placement and low centre of gravity.
Another point to make is you can be braced for impact from one direction, but not others. For example when standing on a train or bus, you can brace yourself for when the vehicle breaks and accelerates with one stance. But you must turn 90 degrees to brace yourself for sharp turns.
I would ask Bohemia to create some fancy equations based on stance, direction of force, direction target is facing, movement speed, range and calibre. This would help decide in a quantifiable (and therefore programmable) way, how players and AI react to being shot.