[Finalgenesis]

I've found truly effective use of AoE evoc to involve either a) suitably immune troops or at the very least appropiate ward/antimagic, b) very high precision (wind guide, eagle eye) with a smaller AoE (pillar, Tstrike), or c) premptive hit in round 1-2 before the army joins together (shadow blast ...etc). For short range evoc I tend to spend 1-2 rounds buffing before getting in 3-4 turns of evoc (luck, eth, quickness, blessings, eagle eye ...etc)

Either way you're limited to 5 turns of controlled spell casting, after which you can count on AI spell casting to be worst then useless 80% of the time.