Confirmed this, Flan does max at 20.
I should know this pretty well, my starter team used to be Remi(Mid), Flan(Near), and Ran(Far).
Flan was trashing everything she could get at with Ripples Of 495 Years, Remi was dropping anything she could(Though she tended to miss a lot, even with a beefed-up HIT.), and Ran was the ranged bombardier with Fox-Tanuki Youkai Laser, and refilling Flan when she ran out of castings of 495, via Nine-Tailed Strategist.
Of course, I also used Sweet Game and Kokkuri-San's Contract for the +XX% Damage Received debuff, it was amazing landing both for magnified damage, then dropping the Youkai Laser, or Ripples.
That team's still my backup beatdown team, I would usually use Kaguya as the supporter, so that way any damage I did take would be rather low.