What I have noticed is that this is not a real "parry" cause It doesnt reflect the damage you are hit or any % of It.
So this hit that people call parry, is a death missile hit that the vizier deals when It recibes any damage. So using poison/ energy or other bombs actives this hit more often. What I Haven't noticed is this theory about the "chain" effect that you Talk about, I thought that the hits were pretty constant (over 500-600)