If it is any consolation, leveling with a box blade on a conventional tractor with 3PT hitch is no joy, either.
If you leave it in float, it tends to ride up and over piles of material.
If you leave it rigid, it tends to rise and fall with the tractor.
The best method I found when I was leveling areas on our property after major excavations was twofold:
One, a heavy box works better in float mode. The weight of it helps hold the material in the box rather than letting the box slip up over the piles. Use the box slowly in float to move large amounts of material from high areas to low areas.
Two, with the box in float, mulitple high speed passes over an area will help level things out faster than slow, methodical, tedious manual raising and lowering of the box.
Anyhow, that's what worked for me on my 3PT hitch tractor.