The text says

causes Increases and Reductions to other damage types in Large radius to be Transformed to apply Fire Damage

that's not just elemental damage! That includes physical. https://pobb.in/oVAKgy7wPXxy maybe? Is there something? I put in a custom modifier to increase fire equal to physical increase -- I was able to pick up 362% increased which is nothing to scoff at. The only problem I can see is the fire attacks I can find are all converting 50-60% physical damage to fire so that decreases quite a bit the efficiency of doing this. But maybe I overlooked something. Or it's still worth doing? Not sure. Anyways, it's just a thought :)