DepthCharge:
As others have posted, the problem is the change of angle because of the tires going up & down in the ruts. If the tires are level, the grading will be level. Visualize a washboard (draw a wavy line on a piece of paper). Now draw your tractor in. Playing with adjustments on the top link can help. Going slower makes it easier, etc. But you still have the fundamental problem.
But you can see that by "pushing" instead of "pulling", the tires are running more level as they are riding in the more level gravel/dirt (or whatever you are trying to level). It's a simple issue of the geometry. I didn't like the regular box blade set-up myself, so I bought a roll-over type. The "box" can be pulled, or, rolled over easy with a lever and pushed as needed. The rippers are in a third position and "rolled" into position without the box blade so you can rip without blading. While a bit more expensive than a standard box blade in my view they are much more flexible for leveling work. The leveling work I have done so far would have been much harder and involved a longer learning curve with a standard, fixed box blade with manually adjustable rippers.
JEH