Runesmith - x% Increased Fire Damage Per 1% Fire Resistance Above 75% appears to do nothing

Finally got the runes to smith up my axe on an ignite build, and as per title, it appears to do nothing. I should have picked up around 2000% increased damage, and gone from "can sorta do t16s" to "obliterate". I am still stuck on "can sorta do t16s".

Flipping Purity of Fire on and off does nothing to tooltip ignite damage, and there is no change in observed behavior in combat, either. Did attempt crafting on fire damage, in case it scaled local fire damage, no love there either.

please add it to the issues list so I can maybe de-mothball this character later in the league.

It function like 7-10% fire damage per 1% max resistance over 75%, capping at 90% max res. So at most it gives 10% x 14, 140% fire damage. It does not specify uncapped fire resistance.

Tooltips not working is not surprising. A lot of conditional things do not change your tooltip DPS. And without seeing your character, if you're already 90 max res without Purity of Fire, then changing the aura on/off has an expected no change to damage.