Not sure i am interpreting correctly, but what I think is happening is you are triggering the IG boss passive twice, once at 60% and then on the CA at 45%.  I don't think it has anything to do with max hp reduction. This has always functioned as such.

More curious as to skullcrown in destroy set 🤔 in general?

Lol, for FW?

Yeah initially it was for FW, but then it turned out the gear was pretty damn good in general lol.

And definitely not hitting 80% to 65% from the one attack - at least not the "traditional" way. Her attack doesn't do enough damage to bring him down that far.

I've been using skullcrown for this faction IG tournament, but haven't paid attention to the auto runs. I will try and watch and see if it happens sans destroy gear (I will not regear in destroy 4u, maybe Quinn will lol)

How much max hp does boss have? If boss is at 61% before initial skullcrown hit, possible the 2 attacks could do enough damage? Warmaster or flawless masteries?

I just missed the entire boss fight typing this, lol. No data point from that run :)

Nope, I won't. lol

Nor do I have a Skullcrown to test it with. :D :D

Is "this repeats until everyone is dead" an observation of your fight or a theory?

I don't understand the whole setting. Why does Skullcrown "counterattack" if she has destroy gear? Ok, maybe there is a chance for counterattack from Retribution or Deterrance masteries, if the IG breakpoint attack triggers the needed requierements. But how will this work until everybody is dead? 

Or is "counterattack" just a mistake for the extra hit? She should not do a third one, wether the target has more than 50% hp or not. One attack, one extra hit if the target has more than 50% hp after hit no.1.

Masteries, correct - and the "until everyone is dead" was just an exaggeration on my part, because even a single recast is enough to wipe the entire team out usually, since both of the minions are alive.

Anyway - IG was really just an example here, to demonstrate the somewhat surprising interaction. I didn't mean to draw special attention to it. The intention of the thread was more to highlight the somewhat misleading text on the abilities, since they simply say "Places an extra hit if the target has more than 50% HP" (or less than, for Sinesha). It should probably say "Places an extra hit if the target has more than 50% of their current max HP" (bold added by me).

Could be that with everyone he is referring to his own team...