what if injury cap on limbs/extremities was applied to damage used for Knockback?
 

It seems like you get knocked back just as many yards when hit in the chest as when hit in the hand/foot or forearm/shin or aftarm/thigh.

It seems like knockback ought to be less extreme when you're not hit in centre-of-mass as that would just throw you into a spin (rotation) rather than launch you directly backward.

Capping the damage you could apply based on HP fractions seems like it could do that.

To balance that out, maybe instead of the DX check at -1 per yard of knockback, all knockback-capable attacks could result in DX checks to avoid falling down at a large basic bonus (like +10) penalized by -1 per 1/10 HP of Basic Damage, but limb hits double that penalty (harder to keep balance when launched into a spin) and extremity hits triple that penalty?