Question about Mages and Gems

[Hatlock]

Hey, so I was trying to follow one of the strategies described in the manual involving using Longbowman and a mage that can cast Wind Guide. As I understand it, with spells that require 100 fatigue, you need a gem the same type as the spell (an air gem) I've loaded some mages with these air gems, each of them a path of Air-2, and I script Wind Guide, but most of the time they won't cast it. Am I making a mistake?

I'm playing Late Age Man.