OK, I was wrong about the power of the foot. I begin to think that this design has been around for hundred of years, why would that be if using the foot pressure was unstable.
Floppy the jaw as Dad One suggested combine with only a modest amount of foot pressure held a stave very securely and I found it quite comfortable. I will still enjoy tweaking the design but if it get too complex it will, much like my horn bow project, never get done.
The biggest question now is do I build it from all my 2x4, 2x10 scraps or do I get some nice redwood decking material?
Also, do I make the legs rigid or removable?