For best ground handling (ignoring the tendency to nose over) the gear should be just slightly ahead of the CG. This will make the plane very suceptable to nosing over if the wheels hit a minor obstruction though. If the gear is to far forward of the CG, landings will be difficult; the plane will want to bounce. The placement will be a compromise of these two condition. On a 40 sized plane, I like the gear about 1.5 inches ahead of the CG.