Exponential?
David - The way I handle that is do an elevator offset mix. I just open the mix when I'm flying and get the plane inverted. Then I adjust it until it flies hands off inverted. That mix gets put on a switch. Simple. I also usually fly with a fairly rearward CG so usually it's only about 2-3% which isn't enough to make a huge difference in the expo setting. At least I never noticed it.