I did talk to Bob Payne today.
Now, I am at somewhat of a disadvantage here because I won't be in the same location as my tractor until this weekend.
Bob told me that he felt the source of my problem was that the bucket on my backhoe was too thick, and that the raised portion under the clamp was probably not contacting the bottom of the bucket.
He had two solutions for the problem I encountered. On his end, he is adding a warning to the description of the hitch receiver that it is "not suitable for backhoes."
For me, he suggested that I shim under the clamping surfaces with a piece of
wood !! Specifically, a 1 x 4. I didn't argue with him, but I am not as convinced as he is that relying on the compressive strength of a piece of wood is going to produce the safety that I really want.
I did not argue with him, or challenge him on this, and I will look at the situation on the tractor.
He is certainly personable, and I believe that he does stand behind his products. OTOH, he described the testing he did with the hitch receiver (pushing his trailer through snow), and I do not believe that this is nearly as strenuous a test as having a 2200 lb trailer uphill from a tractor on a 15% slope.
Right now, I have too many other things going on to worry a lot about this issue, so I will look at the fit as Bob suggests and will probably drop the whole thing. If a shim will alleviate the problem, I will use a steel one, not wood, and I will still limit the use of the hitch receiver to level ground. I will also figure out way to attach the trailer safety chains to the grab hooks on my bucket.
The other thing that happened is I bought a set of hitch alignment balls from Harbor Freight
Harbor Freight Tools - Quality Tools at the Lowest Prices, and these make attaching the trailer to the real hitch on my truck so easy, I don't need the Payne's hitch receiver.
Getting the trailer on the tow ball is now a one man operation.