How to proceed in designing a catapult glider with maximum flight distance?
Two parameters are important to arrive at a good answer, but not covered in your question:


What is the size of the glider? The Shuttle model will fly at Reynolds numbers in the order of a few ten thousands, which puts it in a flight regime quite different from that of large, man-carrying aircraft.
How much kinetic energy will be provided at launch? One advantage of the Shuttle model is its large volume relative to surface area. This allows it to start the glide with more kinetic energy when compared to the model of, say, a glider. In the end, it is more ballistics than aerodynamics which can explain the gliding distance.


The optimum configuration will change with the absolute size. Aspect ratio will grow with size, and a high ratio of mass to surface area will yield better results. The Shuttle model has a weak spot, however: Its large base area will result in flow separation and high base drag. A streamlined body should be better at all sizes.