[Avocet]

Are the OP's seats electric or manually adjustable? I notice the electric height adjuster on the Aventura spec cars is two separate motors - one to lift the front edge of the cushion, the other to lift the rear. Is it possible that the OP's seat is only adjusting one or the other end of the cushion? Mrs. Avocet is 5' nothing tall and the seat goes high enough for her.

Also, worth being VERY careful with aftermarket seat bases. The seat belt buckle is on the seat, so in a crash, the belt loads will partially be dissipated through the seat frame and runners. It's a ferocious pull when you type approve a car, and I think some of the aftermarket guys probably won't bother to test them in the original application.