Poe 2 questions… don’t know if there is a better place for this.

So I have have playing a titan in poe 2, I’ve been using grenade skills for clear and then very quickly figured out I need single target dps so I decide on ignite hammer of the gods. It was work pretty amazing thus far, I’ve pretty much much been one shoting pinnacles bosses untill I hit like tier 3. This where all my questions started popping up. So thus far I have only been using one mace, if I got giants blood and use two does it actually do more damage? Hammer says it hits twice and each hit does 30% less damage, are those two hits then combine into one though, because if not then it would gut the single hit and thus the ignite and I kinda feel like that’s what happening. I’ve only tried a couple bosses but it doesn’t feel like it’s doing more damage. I thought it would be a massive boost. Next question I ran into is why do different bosses seem to have such different stun threshold. Playing titan heavy stunning is a big boost to my dps. Arbiter and king of the mist and the expedition boss all seem to stun way easier than Xesht for some reason he is why harder to stun which I don’t really get. Some of the map bosses are like that and it thematicly makes sense, like forge and abyss. They are both huge so thematically I get it, but in pinnacles I don’t really get it, and as far as I know it’s not something you can look up like a bosses fire ress or chaos ress or hp. Last question I have, a recently got a black flame ring which makes it so my ignites deal chaos damage. Now I’m running avatar of fire so I can only do fire dmg so at first I thought this would make my ignites deal zero dmg. I tried it on a boss and that’s no the case, it worked. So if that’s the case, I’m curious how the interaction actually works. Would the only thing this be good for is that a lot of monsters or bosses have ele res but not chaos, so by the damage changing once the hit has already happened, it’s just like a way of avoiding res? Or like if you have expose, I inflict fire exposure for the ignite, but then the monster takes chaos damage, does the fire exposure still do anything? Would lowering their case res doing anything?
This probably should all be different posts but I’m on a phone so I didn’t want to make 3 different posts =\ lol