Did some testing in the backyard test facility today.
The 1.9's sunk and dug in immediately so went back to 2.2's. These solved the traction issue and the gearing is OK.
Some videos of the first runs...
https://www.youtube.com/watch?v=pk7sHrLft6M
This design seems to do a better job in the loose stuff (paver base)...
https://www.youtube.com/watch?v=yWDPGXH2aS4