HTR,
Watching your learning curve reminded me of mine last year when trying to "figger out" the box scraper! I didn't know the box (3-pt) floated either. It wasn't until I watched a buddy who has probably dragged his box around his horse property a few thousand miles...
When the box is laid down and the lever sunk to the bottom, the box has the most freedom to float. If you have someone else drive slowly and walk behind as the box begins to move, it will dig in until it fills up, then it will rise and "float" on the dirt inside. Except for the spillage out the sides, it will not displace any material once it gets full, except what it moves a foot or so in the "scrape and dump" cycle.
I share your frustration about leveling. Some of the suggestions are great ones but on a driveway with concrete curbing I am limited with one way or the other. I have a wonderful "roller coaster" going on and I have tried a zillion methods to attack it. The best was running in reverse using the rear blade to cut away the bumps. It took adjusting the "angle of attack" of the box to level on the ground. For some reason, my box sat front lip down about 2" from the back. I adjusted it so the back was about 1/2" to 1/4" higher than the front lip. That way it "cleaved off" the start of the bumps. I am going to reverse that when I get a longer upper bar so that the front lip is an RCH (technical term for very tiny amount) above the rear. That way, moving forward, the front lip will cut any bumps off. Who knows, perfectly level may work out to be the perfect setting.
Its fun playing around with the implements. I have decomposing granite on my driveway as well as in my horse arena. I bought some fan rakes and am going to try and weld up a lightweight rake finishing drag for that material. I'll post my results when I get time to get to it.
Play with the pitch of the box when you get one, be careful, and have more fun. Diesel is cheap!
Ray