I know that some BLM have a hard time switching things up and getting used to it. As a SCH in Keeper of the Lake I helped with a BLM who was using Fire III spam until OoMP and then Blizz III spam to full and then Fire III again. Another recommendation outside of working on this rotation is making sure you move the least amount of time as possible. As BLM in FCOB working on T13 (6% why), the only times I move in T10 are when A) Wild Charge, B) I have no heat lightning debuff and need to soak, and c) moving into the middle to deal with Adds.

Typically if I can't switch to Umbra III and I can't swift or proc any casts while moving, I will scathe or transpose into Umbra I. This way when I can cast I will be ready with mostly full MP in Astral phase.