The problem is that Fire IV doesn't refresh Astral Fire, so after 2-3 Fire IVs, you have to throw in a regular Fire, which is 180 potency, or just a Fire II. Also, Fire II hitting more targets gives it more chances to score direct or critical hits, but that's unpredictable anyway.
Whatever the case, in Sirensong, a BLM's AoE rotation should also include a Thunder II every once in a while, whether on proc or hardcast, and Flare.













