The math looks like this:

Fire damage reduction = Clamp(SR% + FR%, 50%)

So if u already have 45% SR mitigation, all u can get is the last 5% by either a lot of extra SR or a little FR.

The advantage is that FR gear has twice the value on gear and that the value reduction after softcap makes it easier to hit the hardcap with mixed SR+FR gear.

So at 1700 SR u hit the softcap and are at ~33% mitigation, now u just need a extra 800 FR, which is not yet affected by diminishing returns to hit the total 50% hardcap.

On the other hand if u can reach 2300-2600 SR after softcap, than i would not bother adding extra fire resist gear. U could still reshuffle some gear/skill in this case, to reduce the diminishing returns effect.

In practical terms lets assume the worst case of a medium armor vamp user:
1100 SR = 23% spell dmg mitigation (base v1 value)
1000 FR = 21% fire damage mitigation (cheap purple FR rig)

So we get a combined 44% fire mitigation, adding a extra 1000 FR ring is not a good option, so either leave the setup this way or add a extra 500 SR ring, which maxes FR mitigation and adds a extra 10% mitigation vs all spells.

Is some fire considered physical damage?

Yes there is a rumor that some fire skills are mitigated by armor rather than SR. Would be nice if someone could confirm this and if in such a case (FR% + Armor%) or only Armor% is used.

Jaxom wrote: »

Is 2500 resist the point we are trying to hit? IE 1700 SR and 800 FR is the same as 1500 SR and 1400 FR? Just trying to understand this.

Here is the estimated math for armor/sr. (Thx to : tamrielfoundry.com/topic/damage-mitigation-formula/)

Mitigation = (6 + 1.02*Armor) / (4600 + 0.2876 * Armor)
https://desmos.com/calculator/5a9uqhawtu

We don't want to actually hit a specific raw value, but a combined resulting mitigation value of 50% or close to it if possible.

The 1700 SR is the softcap, so any SR added above this point is effected my diminishing returns. So a good idea is to now use the still unaffected FR value to get the combined value. So yes as long as both SR/FR are not "overcharged" aka softcapped, u can just add the raw values together until u reach ~2500 in total.

So yes 1700 FR + 800 SR has the same result for fire spells.