Damage from common is 20 from front and 10 from behind on Expert. This is controlled by the cvar z_hit_from_behind_factor, but for some reason, use a value higher than 1 (1 means behind and front damage are equal and the default value, 0.5, means attacks from behind does are half as much damage as from the front) causes instant deaths to survivors. If someone could handle these values better so that attacks from behind are MORE damaging than from the front, it would be very helpful. I am interested too on edit SI attacks damage.
https://forums.alliedmods.net/showthread.php?t=335442