[2020] How does torment really work?

Last (expiry) tick of every individual stack always getting double damage - fine. Sometimes feeling like it's rounded up to 50ms to match movement - also fine. But that only results in nice-ish numbers on the golems. Matthias, Cairn, Overseer, and probably every raid boss is getting 50-90% more torment on actual than my sim. Easiest way to see what I'm talking about is to open a fresh W4, run up to Cairn, dodge his first meteor swarm, put a single stack of torment on him via autoattack, and stand still. Most if not all of your torment ticks will show as double (this ignoring the 10% damage boost your condi's get that is neither a buff on yourself or a buff on Cairn, at least that's visible to the client).

According to transform data, he does not move. He does not rotate. But he's taking double damage from torment. It is not tied to him using skills. It is not tied to him dealing damage to players.

pls halp i'm going insane