[Saulot]

If the important spell is the first one scripted, you can go with just the base gem requirement. In your example and otherwise, it's generally a good idea to give extra.

IIRC, it's also an important thing to consider that mages won't use more gems than their level for certain purposes.

AI gem use is a tricky subject, and mostly receives complaints when it does something you didn't want, but nobody considers it when it does what you do want.