Describe the solution you'd like
For CRAFT events the item crafted is the one that triggers xp gains, while for SMELT it is the input item rather than the output item. This would add a new event SMELTED (or some other name) that is triggered with the output item in a furnace / campfire / blast furnace instead.

Why is this feature needed
This would give similar functionality to craft, allow even more configuration by modpack makers, and potentially reduce configuration for modpack makers. If charcoal should give the same xp no matter what created it, you would only need to define the SMELTED xp award for charcoal and none of the inputs.