Is there a way to make an enchantment on a shield reflect damage only if the shield has been hit?

As I have it now, damage is reflected any time the player is blocking. However, attacks to the player's back do more damage to the player since they don't hit the shield, and therefore return more damage to the attacker than a blocked attack.

Either making that reflected unblocked damage reduced to the same amount as blocked, or making it reflect zero damage, would be acceptable.

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I doubt this will be answered at this point, but I've noticed Reflect Damage does not account for ANY damage absorbed by armor. If someone could figure out how to make it reflect a percentage of the base damage, before armor or blocking is taken into account, that would be ideal.