Inevitable Demise bug?

As I see Inevitable Demise count wrong.

So, the talent says, 15% dmg increase to Drain Life every stack. Its okay, works good.
But the Drain Life spell says: 500% Health increase from the damage.

So if you get the 50 stack it dmg ~25k its good. But the Healing amount of that is not 500%, cause its heal only 47k. Its only the 100% or maybe less a bit. This is a HUGE BUG.

I’ve reported before, but I looking for some better exped players to correct me if I’m wrong.

The healing bonus of Drain Life is decreases by each stack of ID, you can check the tooltip of Drain Life while ramping up your ID stacks, the 500% Healing is decreases with each stack. Its prolly b’cuz it would be too OP i guess to heal 400-500k with a Drain Life on full ID stack, imagine it with the Grim Feast, Soul Rot and Accured Vitality synergy, it would make Affli an unkillable literal demigod in arena.