Gem Usage Quirks?

[Ironhawk]

So, what your link says is that the gem restriction only applies to gems used for fatigue. The cost can be paid by any mage of any power (assuming they can cast the spell in the first place).

Ok. But then how do you explain the fatigue of the caster? If the above information is correct he could have used 5 gems (aside from the costs of the spell) to break down the 500 fatigue of the spell easily.