Crystal Shield

[thejeff]

Wait a second. Are you saying actual battlefield placement? Where on the map you put the mage?
It's certainly not dependent on that. As far as I know nothing is.
Order of action on the battlefield seems to correlate to the order they're listed elsewhere (F1 screen, Army setup, province display). This is also the order ritual spells are cast.
It may be unit number, but it's not strictly the oldest units first. Are unit numbers reused? That might be it.