So whenever we're insufficiently skilled at a skill tree we get an increased AP cost of 2AP per tier of skill we're short of in the tree. So a lvl 1 air user would have to pay 12Ap for Invisibility while a lvl 3+ pays 8. Yet once we're overskilled for that ability the AP cost stays the same. Headvice on a lvl 5 air mage costs 6ap just like a lvl 1 mage.
I'd suggest a system where the AP cost is reduced as we get more skilled at a tree, and maybe a lvl 5 talent like Marksman has but for all trees. To keep AP costs from getting crazy low, how about -1AP per 2 levels of the talent tree you're surplus by? So Headvice at lvl 3 becomes 5ap, and at lvl 5 becomes 4AP. Or Invisibility at lvl 5 goes from 8 to 7AP. This keeps the powerful lvl 4 and 5 skills from getting cheaper (if no lvl 5 perk) while letting us possibly fill in an extra weaker attack per turn on a caster.
Every 2 points into Int lowers cooldowns, figure there's nothing wrong with lowering AP costs too somehow.
