Shifting weight works great in hang gliding, not so much with modern airfoils used in our glass slippers. Pegasus had a weight shifting system in their D model, never heard anyone say it was worth the effort. 7V told me he pumped the mercury aft in Dick Brants Nimbus-3 and left it there! I rigged up a 10# lead weight that slid inside a 3” plastic pipe to see how the Genesis-2 handled with the CG near the aft limit. I flew with it for a year, couldn’t see any noticeable benefit by shifting the weight forward in the run. An aeronautical engineer who’s also a glider pilot told me it’s best to put your CG at about 85% (or more) and leave it there!
Hope this helps,
JJ