If the ground effect is amplifying, then it's going to amplify the lower wing's problems more than the top, right. And if it's ground effect amplification that's the major player, then any solution could employ ground effect amplification and be less obtrusive outside ground effect, right. So wouldn't you want the trim tab to be on the lower wing in order to work in the amplifying ground effect? And if you didn't place the trim tab in the "better" environment, wouldn't it work less at the times it needs to work more? and have too great a negative effect than necessary outside the ground effect envelope?

Embracing your argument would lead me to do the trimming needed, but do it to the lower wing. It after all should be experiencing ground effect sooner and stronger. And since there are strip ailerons there, and it's easy to trim them with the TX, I would expect them to be more than adequate for the required trimming. And that trim, when adequate in the "enhanced environment of ground effect", should be less upsetting outside the ground effect.

You've introduced an interesting "new concept". It's been fun discussing it. Hope we all learn from the discussion.