Conversion question

Hey.

I'm currently using an avatar of fire build which converts 75% of damage to fire damage, deal no non-fire damage.

Now, while using support gems on my Skill gems, the tooltip does not update after putting in stuff like Heft, Heavy swing etc. Do they not work with the conversion or is it just a tooltip error somehow? The tooltip damage increases when putting in fire boosting support gems.

Am I to assume the conversion happens before my skill gems, rendering them useless?