Wayne & Tin-Bender,
Regarding the situation where the truck rear is pointing down and so is the tongue of the trailer, I think swiveling on the ball (as Tin-Bender suggested) may explain it for the PP; however, I have the Hensley and I believe the struts are going to prevent swiveling on the ball. I can't explain it for the Hensley other than maybe the struts prevent such a situation. That is, the entire assembly will always be in the same plane.
Or maybe there is enough play between the upper and lower head assemblies.
Maybe someone else has something to add.