I don't know if you need to remove sharpcast, but it would be nice if Fire IV could contribute to the proc so fire I could essentially be replaced with fire3.

It does seem a little silly to cast big explosions and then one tiny little fire bolt to keep the explosions going, Would be more fun to cast a Fire III with a high potential of it being instant. You could adjust the mana/potencies to fit and not be OP. For instance maybe Fire III procs from Fire IV still use the same amount of mana so you don't get an extra fire IV out.

Right now Fire III is mostly just to get into the AF rotations and for movement when you get a proc.

I think it's a much better looking and more powerful spell that would be nice to use a lot more.