AI for Mages Using Gems

[DonCorazon]

I am trying to figure out how many gems I need to give a mage who is going to cast 2 low level buffs for which he has the skill and then a big spell that costs 3 gems and will need 1 gem to give him the skill necessary to cast (buffs and big spell are all in the same school).

So if I give the mage 4 gems, will that be enough? My fear is that the AI sees he has the relevant gems in his inventory and uses them to reduce the fatigue cost of the 2 buffs he is casting so when it comes time for the big spell he won't have enough gems.

In that case, I guess I would need 6 gems - 2 that the AI will burn on his buffs (even though that is not what I would want), 1 to boost him so he can cast the big spell, and 3 for the big spell itself.

Thanks