Mostly likely you're getting the nose pitching down in your rolls and end up needing lots of down elevator coming thru inverted to keep them straight. It's a Cg issue most likely. Had the same problem on my TopCat jet until I took some ballast out of the nose. The the rolls cleaned up nicely. Seen it on other airplanes too. Get your airplane to where you only need slight forward stick when inverted, then see how it rolls. Then go for the other suggestions.