Originally posted by nature valley:

After H&H, how much HP you have also plays a part in how much damage you can block/parry.

No it's not HP it's "Stamina". Less Stamina the more of the shield damage will increase which will break the guard of that shield. Though I use regular shields and not tower shields. It should be Stamina depends on how much you have before the shield is broke of guarding.

HP has nothing to do with that and only helps the player's characters get far in doses of unguard damage by later enemies depends on what food the player uses.