Shoe still has me thinking about Tall Paul's cool experiment. I remember as a kid I used to like the window seat just aft of the trailing edge on commercial flights because I could watch the terrain and control surfaces of the wing. Just as the plane touched down the pilot would nail the throttles open and huge clam shell deflectors would swing around to reverse the direction of the engine thrust and slow the plane. I still think the ground plate is merely a deflector that is redirecting the thrust of the rotor 90 degrees.

If this is right, the helicopter's lift will increase as the distance of the rotor to the ground plate increases even if you increase the size of the deflector proportionally. At some separation distance (1 m?, 2 m?) the ground plate should have no influence at all on the system. Any weight added as a consequence of increased distance or ground plate size could be subtracted from the new scale reading.