I don't know if this is applied, or not (I imagine it is to some degree), but BF might be missing some sort of Layer in all their Calculations.
Example; One Layer of Calculations is for Fire against Troops in their current Stance, and another added Layer for said Troops who are showing situational awareness within their current Stance (Ducking, Dodging, etc). So, if a Bullet or HE Frag Trajectory intersects with a Vet Trooper in Standing pose, then he may get a Better Savings-Roll (chance of survival) compared to a Green Trooper in same Standing pose.
*Overview*...I mean, after all, there is a reason why a Vet Trooper has survived the War up to this point.