Combustion

Enemies ignited by a supported skill will have reduced Fire Resistance. Since it's possible to stack multiple ignites my question is: does it have to be the active ignite, dealing the most damage, which can apply fire exposure or can Combustion be used for ignites from lesser sources that may not deal damage.

Minus resistance is not calculated like poisons or ailment damage when only a singluar instance is allowed.

As long as the linked skill is the one applying the ignite, the minus fire resistance takes place. If another ignite comes it with higher damage and overwrites the ignite, the minus to fire resistance should still be there.

I am not sure how long this debuff lasts however, you may have to reapply the ignite every 4 seconds (typical time for things like this).

Also this debuff is technically different from "exposure" as it doesn't say that explicitly.

My understanding is that this mechanic works similar to elemental equilibrium, but for fire specific conditions.

As long as you hit with the attached skill, the -max fire res should take affect. I am guessing that -max res would need to be refreshed on meatier targets, but I am not 100% certain there.

Well, default ignite duration is 2 seconds so the duration of the fire exposure debuff should be the same.

I am aware that another ignite with more damage will "overridee" a previous ignitie with respect to inflicting burning but previous ignites will be still present for the duration and run their course. The question is, if the ignite with more damage was not supported by Combustion will the debuff caused by a previous ignite still be active. Same goes for a newer Combustion-suppoted ignite with less damage which can be applied but cannot deal burning damage while a higher damage non-Combustion ignite is doing the deed.