Basic fatigue question
I am confused by the battle spells that are extremely high fatigue and the exact mechanics on lowering fatigue. Lets say a spell is S7 and 700 fatigue, and I want to cast this with an S6 unit (including all path boosting items). can someone do the math on how this works with gems?
I can use 6 gems max correct (because I'm S6). Is that a gem limit per spell or per the entire battle? Anyway, assuming I use 6 gems simply to cast the S7 700 fatigue spell, I understand that the first gem makes me S7, but that's the highest path boost I can get. So what do the other 5 gems do to the fatigue number? Or does fatigue 700 mean I have to use 7 gems, in which case an S6 unit simply can't cast it because an S6 can only use 6 gems??
Similar but even more basic fatigue question: Lets say an F3 mage is casting Flaming Arrows (F4 fatigue 100). If he uses one gem to get to F4, can he cast the spell for 100 fatigue? Or does he need two gems because the spell requires the use of one gem?
As you can see I'm pretty confused on this, thanks for the help.