Quote Originally Posted by StouterTaru View Post
It will if that DoT extends the time for your rotation.

Optimal AoE (15 seconds) - Transpose > Fire 3 > Fire 2 > Fire 2 > Repeat
Add in Thunder (18 seconds) - Transpose > Thunder > Fire 3 > Fire 2 > Fire 2 > Repeat

It won't cast quick enough to not extend your rotation by 3 seconds. It won't take up enough time for you to get a 3rd tick of MP under UI (another Fire II). Someone else can figure out the potency change, but I can tell you it is a substantial drop.
You forgot Flare...