Question: How does Reduced Elemental Damage stack in game?

So, I am running a super elementally heavy build and I want to be able to run SOME reflect maps (e.g. accidently hit Atziri's Queen of the Vaal reflect clone and survive). So I looked into elemental reflection reduction and obviously Sibyl's gives you 80% reduction to elementally reflected damage, so that means only 20% of the damage that is reflected to you matters (e.g. 14% reflected of 100, then 80% reduction on that would be 2.8 from the 100 you dealt), now if you get Exposure Tolerance and the smaller nodes leading to it then you get 2 sets of 15% reduction and one set of 30%. My question is do these stack additively or multiplicatively, e.g.:

Lets make new numbers, so we deal 714 elemental damage, so reflected (unmitigated) we get hit for 100 damage.

Additive our reduction would be:
100*(1-(0.8+0.3+0.15+0.15)) -> 100*(-0.4) healing for 40? This seems unlikely to me

Multiplicative would be:
100*(1-0.8)*(1-0.3)*(1-0.15)*(1-0.15) -> 100*(.2)*(.7)*(.85)*(.85) -> ~10 so you'd still take 10 damage or 10% of the damage originally dealt to you. (your reduction to reflected damage is 90% effective)

So short and sweet does anyone know if the math behind reduction to reflected damage taken is additive or multiplicative?


Thank you for your time and input.

Reduced and increased modifiers are additive, even those as exotic as reduced reflected damage taken.

80% red. ele reflect taken + 30% ele reflect taken = 110% (eff. 100%) red. ele reflect taken = immune

More than 100% reduced should have no effect, but I'm only 97% sure on that one. Why not do some testing?

Testing is the next obvious step, I am just trying to plan my respec, I started out with a hybrid build but am switching to pure elemental with energy shield. It is a decent journey to pick up the elemental reflection in the form of Exposure Tolerance and I am trying to save on "orbs of regret" if I don't need them.
But your take would be that it is additive, would basically be:
100*(1-(0.8+0.3+0.15+0.15)) - IF (0.8+0.3+0.15+0.15) > 1 then 1 > 100-100=0.

If anyone knows for sure, I'd love a definitive answer. If no one comes in knowing for sure, I'll test as suggested and post the results upon completion.

Increased/reduced is additive. More/less is multiplicative.

And being over 100% reduced isn't necessarily a bad thing where the reflect mods are concerned, as 100% reduced isn't outright immunity. Anything that would increase your damage taken, such as shock/shocking ground, will negate a portion of your reduced reflect. You can still end up nuking yourself in those situations if your DPS is high and you aren't careful.