[2019] Cast When Damage Taken does not trigger exactly at its damage threshold.

I discovered this (rather unfortunate) fact with my attempt at a Scold's Autominer. My Volatile Dead Mines cost 132 mana; Each use deals 528 damage to me, and I have zero physical mitigation (no armor, no pantheon mitigation). Level 1 CWDT has a damage threshold of 528 damage. I tried unspeccing Zealot's Oath (so I had zero regen at the time of use) but that doesn't do anything, either