So, myself installing a Summit 3rd function, I called Summit and spoke with them. The power beyond is fluid exiting the valve, no matter the valve, FEL valve or 3rd function valve, it moves on to 3PT or rear remotes or BH then back to tank.
Plumbing the FEL power beyond to the 3rd function P port (power beyond) will make it work in reverse, it should work Summit says. Summit says it was designed and tested to work as: FEL PB > 3rd function T port > through valve and out 3rd function P port back to manifold.
Summit, Land Pride and WR Long all use the same hydraulic schematic as OP mentioned.
Edit: This is plumbing the 3rd function valve WITHOUT a BH or rear remotes