Coal Stoker not applying as expected

Maybe I'm just missing something in what's considered a "Modifier" but it looks wrong to me. I have 105% fire and 25% lightning which doesn't make sense to me given the effect of the passive.

Even if it was capped by my max fire res res instead of using uncapped res the math doesn't look like it works out.
https://i.imgur.com/BNjMlVq.png

lets see. you have -60 base resists

you have 105 fire, which means 165 comes from modifiers

165/2 = 82.5 => 22.5 lightning resistance

each modifier is treated separately so the 2.5 difference probably comes from rounding

Yeah okay, math checks out there, I guess I must have lost res in a gear swap without realizing it. It feels very off to have the practical effect be a quarter of the res on a 50% mod but the math is the math.

when counting practical effect you should consider it starts at -60, which is a big deal

looking on my math further, it does not take in effect 20 resists you gain from quests, which I am not sure if count towards this modifier. Probably not, because it would make the final 42.5, which was my error, sorry for that

lets try it without them

145/2 = 72.5 => 32.5

still does not match up, but 7.5 difference could be in rounding range. But Im no longer sure how rounding works, in PoE1 it always rounded down. Hard to tell further without doing proper research on existing character.

so I at least tell you what it is supposed to do: I should take every single fire res modifier you have, positive or negative, and add half of it (rounded) to your other elemental resistances