I am not sure how the dual rates could of made it worse. Did you switch to high and low to see how it reacted? I know to little will make a good bit of change on how it acts or is able to hold position. That may be a problem.

On the other hand to much expo could make it feel different also. Since in first post you mentioned you added expo also. It could be to mushy in middle to where before it was linear. Maybe you had more responce out of less stick than with to much expo.

I would think you would need very little expo in that type of plane. I would start off dialing in expo at a very low %. Then if it is to touchy add more until you find a good spot for you to keep it at. Now in some cases it is other way around.

Also did you program expo on both high and low rates or just on one rate?