[Nick_K]

I wouldn't recommend using multiple flames-from-the-sky on the same province in the same turn. A proportion (50% IIRC) of the units in that province is immune to such attacks and these immune units are immune for /all/ such attacks in that turn. So, if the enemy has 20 mages, 10 are vulnerable and your first casting kills 7, then there are only 3 left that the second can target.