It takes about 20 to 25 percent expo to make the control response linear as a round servo output has the opposite built in, that is, you're automatically more sensitive at center than at the extremes.

An advantage of expo over dual rates is that the center is softer, while still retaining full throw if you get into trouble.

The Revolver is probably a perfect example of a plane that will benefit from expo on elevator and ailerons. Expo on rudder helps with take offs and landings on planes with a big rudder or a lot of throw to keep things under control.

On the DX7 you want positive+ expo to soften center.

Good luck, thats a fun plane.