Casting flaming arrows

[Thrawn]

He's casting communion master himself, and the other celestial masters are casting communion slave (ie, no matrixes). He's trying to do it in Round 2, the order of spells is something like:

Communion Master - Flaming Arrows - Pillar of Fire - Pillar of Fire - Pillar of Fire - Cast spells

Perhaps this is the key? "The computer will often refuse to cast spells costing gems if it considers the opposition too feeble." - K

I have probably close to 150 archers in that one battle group. Is there a limitation on the number of archers you can cast with it? a balancing thing?