Paul, I believe part of the equation to an elevator's response is the angle of attack change that comes along with the elevator deflection. The hinged leading edge will certianly increase the camber but it reduces the amount of AoA change. But a conventional elevator or the compound elevator maintains the AoA change as well as adding the camber to the equation.

DHG, do yourself and the rest of us a favour and start with a standard rudder and then pull the hingepins and mount up the compound rudder and let us know how it works out. If you need a sketch for a swappable hinge system let me know. I've done some using music wire hinges to allow for replaceable rudders in the past and they worked out great. A bit more work for sure but damn it man, THIS IS SCIENCE!