[OmikronWarrior]

With out looking up specifics...

Base Fatigue/100 = number of gems required to cast, always.

This does not change with boosters, magic scales, or anything. However, a mage can consume an additional gem beyond the spell's requirements, and this will raise their magic skill by 1, which may be necessary to cast the spell at all, or that extra level will divide fatigue.

The amount of fatigue felt by the mage, however, WILL change depending on magic level, drain scales, and encumbrance.

P.S. Also note a mage can not use more gems then they have skill in a path. So, using an A1 mage to spend two gems to cast a 200 fatigue, A2 spell is a no go.