Your perception of how much to load it is probably a bit off, you just need a bit of forward pressure, just enough to take the slack out of the system which the harris legs do pretty well on their own being spring loaded. You dont need enough to be bending the legs back on themselves or anything. And the problem with the harris feet as I see it is that they roll. I went with the tac supply talons but I dont think they exist so the only other option really is the hawk hills. But the point at the center removes the rotational axis from the equation so while the talons can still spin they dont have any radial pressure and stick tight. .
Boltfluter Did you ever get around to designing those harris feet and if so have you looked into making more?