I seem to have finally sorted it. The glider was clearly not symmetric and I had what Dennis P. calls a "cross-tune", i.e. flies straight but isn't set up straight.

I got the tape measure out and measured all the wires, also to the trailing edge. All OK, but the tips still clearly differential by 2 to 4 cm. Decided the only way to sort out the trailing edge was set the left sprog higher, it was also visibily screwed in by a thread or two. Unscrewed it half a turn: better, not perfect. Unscrewed it another half turn: nearly spot on. Flies nicely, a bit more high siding required on the left turn, but that's where the inboard concentric gives a bit more anhedral.

Adjustments so far: right tip set to neutral from 10mm downward (more lift). Right sprog net movement maybe 1/4 or 1/2 turn down. Left sprog a whole turn up. Trailing edge is now near perfect, but I haven't checked the sprog height against the keel yet.

Probable next adjustment: set both inner concentrics up (more anhedral) and then the tips up (rotate concentric down), which should give fast response and a bit of high siding.

9:52:08 PM