[ano]

I could not give four gems because Raksha is level 3 air mage and thus can use only 3 gems per cast. So the only option is giving a booster item (Flight has obviously no sense during storm). This means (as I mentioned above) that this spell seems to be uncastable at all for a A3 mage without boosters once Arrow Fend is researched.
As for the battle mechanics, I just think that scripted spells should never be overridden because of "excessive fatigue". They still should be overridden if the spell cannot be cast or if the opponent army is *too weak* (I think, this is a separate discussion topic) but NOT in the case when everything is ok but the non-scripted spell which AI likes very much (Arrow fend in my case with 220322 score) is cast instead of scripted one just because it causes less fatigue. It makes no sense at all in my opinion.