So I figured out where my 22.5% is coming from (with help from someone at Maxroll). It’s taking 25% of the 90% from Burning Instinct, which is 22.5%.
Also confirmed that Endless Pyre is not contributing to the tooltip at all in-game. Tried switching between 3 ranks and 2 before the BI realization, and it stayed at 82.5% - which also makes sense in light of the BI realization because at 3 ranks Endless Pyre appears to be contributing 0, so it can’t go down from there.
So it looks like, at least for the tooltip value:
- scales with Burning Instinct (but not in a way that would make mathematical sense since ostensibly Burning Instinct should be increasing the overall “Damage with Burning bonus” and that should then get read by Combustion, not itself acting like 90% additive for Combustion, Torch glyph, and the Aspect of Conflagration (Incinerate)
- does not scale (but as-worded should) with Damage Over Time affixes, Endless Pyre (Burning; given that it works with Aspect of Conflagration and sort-of works with Burning Instinct)
- untested but unlikely: Aspect of Creeping Death, Aspect of Engulfing Flames, Glinting Fire Bolt. Each of these increase burning damage but based on conditions local to the target, not the player.
It’s also not clear if some of the things not showing in the tooltip do actually contribute to the damage bonus from the passive but just don’t show up, or if they don’t contribute to the damage bonus from the passive at all. (This also includes whether the higher value from Endless Pyre further improves Combustion against the target when its condition is met, although this is another in the “unlikely” category.)