Spell usage for melee units with magic

[MartialDoctor]

I have been playing with the Yomi recently and I have been a bit confused as to the Dai Oni's lack of spell usage when not scripted.

For example, in a recent battle, one of my Dai Oni was in the midst of battle and had taken quite a bit of damage. I would assume, in the next round, it would have cast a spell, such as Soul Vortex or Drain Life (both were researched), but, instead, it just attacked again. The Dai Oni's fatigue was only at around 18. The Dai Oni's command was set to "attack closest."

So, my question is, is there any way, outside of scripting (since that would be very limiting, at 5 maximum scripts, for an attacking Dai Oni), to have a unit attack and use spells. Or do units set to attack cast spells automatically, if they can, and this was just one of those times the AI decided to attack rather than cast a spell?

Thanks for your help.

P.S. I apologize if this is a repeat of another posting. I searched but could not find another posting of a similar type.