BTW, you might also want to consider moving the trimtab to a lower wing. If it's effect is needed only at ground effect levels, and theory says stuff is more effective in ground effect, then it could be deflected less on a lower wing than on an upper wing. And that detail would help suggest your theory's validity. But more than just backing up the claim, it would also result in a better flying airplane.

You've now got a trim tab on an upper wing that is deflected enough to have the required force in the "ground effect envelope" of the airplane. But it's not in the ground effect as much as the warped surface it's trying to counter. So when the airplane is in ground effect, the trim tab is operating in the less powerful "effect" but the wing is. Also........

When the airplane is not in ground effect, the trim tab should actually be "overpowering". The wing's warp is no longer in the favorable environment (favorable to the warp screwing the aero, that is) when the airplane is at altitude. And now the trim tab is at much greater speed and should be way overtrimming whatever the wing warp can be doing. So your trim tab is set "wrong" almost all the time. And the setting is producing excess roll trim and excess drag.

BTW, did the airplane require any roll trim before and after the trim tab?