I note that going prone only has the effect of lowering your speed to a quarter of normal. Lower speed is appropriate. Still being able to dodge (we've all seen the protagonist rolling back and forth to avoid blows) and make a melee attack (I'd still view a knife wielding attacker on the ground as a threat).
However, there is no improvement to cover. Granted, a prone person in the middle of an open area doesn't have any obstacles protecting them or being sighted on. But "hit the dirt" is has always been a valid combat reaction because it does indeed lower your profile and so make you harder to hit. Perhaps shooting at a prone person should add a Bane die to the attacker's roll?
However, there is no improvement to cover. Granted, a prone person in the middle of an open area doesn't have any obstacles protecting them or being sighted on. But "hit the dirt" is has always been a valid combat reaction because it does indeed lower your profile and so make you harder to hit. Perhaps shooting at a prone person should add a Bane die to the attacker's roll?