[Calahan]

I have a fair idea how the casting AI operates (currently working on a mod dealing with this exact issue). But I'm not going to go into the details of the matter here. Since I don't want the (guaranteed) hassle from any of the *individuals in* the community, and who think they know better based on some random game they played six months ago while watching a fast-forwarded battle replay. (so you can thank them for the reason why I, and other experienced players, no longer share detailed knowledge very often)

But I will say that friendly fire is one of the most overriding issues with regards casting AI spell choice. As in short, a useful rule to remember is that if there's any chance at all of your troops being negatively affected by a spell, then nine times out of ten the casting AI just won't cast it (and it'll often override any such spell even if scripted). Although fatigue spells seem to operate under a different rule set.

And expecting the casting AI to cast Wither Bones as LA/MA Ermor = Epic Fail
(unless you somehow have no undead units on the battlefield yourself)