When an enemy lowers your over-capped resistances, how is it calculated?

If this info is on the web anywhere, my google-foo has failed me.

Do enemies lowering your resistances do so based on what your resistance is capped at, or does it count the total resistance over the cap?

Lets say your fire res is 120%, capped at 80%.
A nemesis lowers your fire resistance by a flat 50.
Is your current resistance now 70% or 30%?

Later, your 120%, capped at 80%, fire resistance is lowered by a percentage this time for 50%.
would your new resistance be 60% or 40%?

I would prefer someone who knows for sure to answer rather than speculate please. This is mostly for killing a couple pesky nemesis in end game content.

Thanks a bunch!

It depends on the type of debuff. If it’s an absolute resistance reduction, it will ignore the overcapped resistances entirely. Some notable enemies that can do this are Valdaran, Sentinel, Anastaria and Shar’zul.
If a debuff has -% resistances as part of the skill, such as the resistance debuff from Chthonian harbingers, it will factor in the overcapped resistances. The only nemesis that I can think of with a skill like this is Zantarin.

I see. So over-capping resistances is useless against absolute debuffs.

Since we’re talking about nemesis debuffs in particular, I appreciate your naming the ones with that type of debuff. It happens that those are the three that give me pause in crucible, so that means over-capping is pointless for me. This news means I can safely redistribute over-capped resistances elsewhere.

Many thanks for your help!

This kind of reduction is nonsense in my opinion. Is there any kind of reasoning behind this posted anywhere?

Not that I’m aware of, but I’d imagine it is done to encourage players to avoid those attacks and place them on the defensive sometimes rather than just ignoring it through gear. Most absolute resistance reductions are pretty easy to avoid even if you play a melee character so it’s not really that bad. I think the only enemy that has an attack which can’t be avoided is Valdaran’s lightning bolt, but that debuff only lasts for 3 seconds instead of the typical 5 seconds.