Self-ignite mechanics - am I understanding this correctly?

I've been testing out alternate methods to Grinning Immolation to proc self-ignite. One idea I landed on is using the self-damage from Infernal Flame to self-ignite. However, I've been running into some problems.

Per the official wiki, "The chance to apply ignite depends on the amount of pre-mitigation damage dealt relative to the monster's ailment threshold. It is a base of 1% chance to apply per 4% of ailment threshold the hit deals."

This means that, assuming an ailment threshold of 50% of my max HP, a pure fire damage hit of 200% of my max HP will always ignite me. It should not matter what my fire resistance is, as we're looking at "pre-mitigation" damage (i.e., before resistance is calculated), just as long as the hit is pure fire and deals 200% of my max HP.

Therefore, if I have max energy shield equal to or greater than my max HP, then Infernal Flame will deal me fire damage at the 100% self-ignite threshold, because max HP + max ES >= 2x max HP, or 200% of my max HP.

However, this does not work in practice. During testing, with 85% fire resist, 1K ailment threshold, 2K max HP, and 2K ES, Infernal Flame does not reliably self-ignite. It does sometimes, but not often. I also tested this with 0% fire resist, and to my surprise, with the same setup, Infernal Flame always ignited me. This means that chance to ignite is based on post-mitigation damage, not pre-mitigation.

I assume this is intended, as the game itself only states that "Fire damage from Hits Contributes to both the chance to Ignite and the Magnitude of Ignite, so Hits dealing more Fire damage Ignite more often, and inflict stronger Ignites". The game never states whether fire resistance is included in this calculation, but I suppose it is logical to assume it does.

So, the wiki is incorrect, right? Or am I missing something important?