A couple flights of my Nardi FN.305 which I built from late Mike Nassise plan. The model has a 20.5" wingspan and weighs about 27g excluding rubber. In the first flight I used a 4g 4 strands of 3/32" rubber, which roughly resulted in a motor length of 1.5x hooktopeg distance. This long motor made the glide quite unpredictable as the slack moved about in the fuselage after the motor run.

The second flight is with a shorter motor which has a length roughly equal to the hooktopeg distance, with just enough slack to allow freewheeling. Multiple flight with this setup proved that the glide was much improved.

I'm now planning to install a rubber tensioner setup which allow me to use a longer motor without the problem of the slack moving about. GizmoGeezer could be a good way to go its weight is not going to pose a problem.