Why does Red Mage need a new tier? Make it based on skill!
As for a suggested formula for Refresh II to make it scale, I wrote up a bit of math.
You can get a current cap of about 376 points with an additional 70 point with a perfect gear set for Red Mage, and 16 points for merits. Assuming an additional seven points per level up to 99, you'd get 404, meaning 420+70 points in perfect gear for 490. However 15 of those points come from the pants so 475 would also be the cap assuming that 15 points means less then +1 refresh.
If the goal was just to keep Refresh II at the current 6MP/tic at 82, the level you get it at, then at 82, you have about 293 Enhancing Magic at cap. A good way to work with this would be having it work like the gain spells, and have skill have no effect below 300. That gives 175-190 relevant skill points to base the formula on, if keeping a base of 6MP/tic. One way to do this would be to have 30 skill per point increase, meaning 490 skill, or 475 skill with the AF3+2 pants would give 12MP/tic.
That said, it could just be made purely skill based - at the same 30 points per point increase this would be a max of 16MP/tic but with no base (but the current amount would be reached at a measly 180 skill). You could also have it purely skill based with a target of 12MP/tic with 40 skill per point increase.
The three previously suggested formulas with maximums assuming 99 cap having no new enhancing gear (unlikely) and a 7 skill per level increase (pretty likely):
- 12MP/tic target with 6MP/tic base: (Skill - 300) / 30 = X, 6 + X MP/tic
- 12MP/tic target with no base: Skill / 40 = X, X MP/tic
- 16MP/tic target with no base: Skill / 30 = X, X MP/tic