[thejeff]

Any gems needed to cast the spell do not count towards raising the caster's level.

So your A1 mage would use 1 gem and (1/(1+1-1)*100)+enc = 100+enc fatigue
An A2 mage using 1 gem would get (1/(1+2-1)*100)+enc = 50+enc fatigue
An A2 mage using 2 gems would get (1/(1+3-1)*100)+enc = 33+enc fatigue
etc...