Hello,
Very nice question, i I only saw this today on the Unanswered Section.
I've killed this boss many times, and most of the time my loot is just a white gem, some potions and some crystal coins. Recently I bought an Eldritch Claymore, a very strong sword that has most of its damage on fire, it's obvious that my participation on this boss (in Damage) has increased and i I noticed that the loot has improved considerably, in considerably. In the first day i've droped I've dropped an eldritch crystal + Brainstealer Tissue, and in the second another Tissue.
So, based on this, i I guess that it's possible that with more damage we can get more loot. (At least in this boss).