question about ai spellcasting

[Janlm]

I just had a large army with alot of spellcasters entering an enemy province. I had prepared them for a major battle. One spellcaster was scripted to cast flame arrow, and others where scripted with alot of other spells required gems, amongst others wrath of ancestors. All spellcasters had all the gems they needed, yet when battle started, the enemy army had moved elsewhere so i only faced a small PD force. The problem is that none of my spellcasters cast any of their scripted spells.

So the question is, does the ai modify its behavior when i meet such a small force and discard my gem required spells? Or what other reasons can there be that my mages decided to disregard their script?