I've attached links to a couple of photos of the fuel return line. Not the best photos. The return line is the lower fuel line without fire sleeve and can be seen returning the firewall bulkhead fitting. This line returned fuel only to the left tank. I did find a restriction orifice in the return line and with my moderately accurate measuring method appears to be a .046" hole to restrict fuel flow back to the left tank.
Using the fuel boost pump to empty the remaining fuel in the tanks, pumped for 30 seconds into my wife's favorite measuring cup, through the fuel return line. Thirty seconds of pumping yielded 200 ml. I extrapolated the 200 ml to be 24 litres, or 6.35 US gallons per hour being returned to the left tank. I expect that during normal operations the recycle rate would be higher as there was very little fuel left in the tank when this rudimentary test was done. Greater fuel head pressure to the pump would likely increase the pump throughput.
I suspect that the fuel return line was installed to provide cool mogas fuel to the FWF fuel system and reduce the chance of vapor lock.
I've opted to remove the recycle line and at the same time fire sleeved fuel lines FWF. For the time being I want to keep fuel management simple and use only avgas. Possibly in future I may experiment with the fuel return line and using mogas, but would opt for a smaller diameter orifice than was originally installed. I think the system has merit, but would require accurate and trustworthy fuel gauges.