Leaders and units - who casts what on whom?

[Kristoffer O]

[quote]
baboune said:

Hummm... There is no way to make sure a specific group is targeted. What goes into defining who is the target for a spell? (offensive or supportive spells).

The spell casting AI takes numbers, HP, protection, resistances, distance, precision of caster and other factors in account. Offensive spells are targeted where the most probable damage will occur, defensive spells where the most number of strong units will be buffed. I'm not sure how numbers and strength of troops compare in this case.