This is also known as 'head tilt'
Some WD OEMs use washers between the shank to head. Others use
washers on the side bolt. Am sure there might be other methods...all
doing the same thing...head tilt adjustment...or as the OP calls it
'Angled Ball Hitch'
Another way of explaining this (different verbiage saying the same thing as others
have written) below
The bars, no matter traditional round bars to trunnion, should be close to level
with the tongue when fully or final adjustment.
That is to provide them the travel needed during driving and the undulations of
the road.
Travel up and down...plus during turns with undulations
Undulations where the setup pivots on the ball. The bar/trunnion will increase
and decrease in tension
That is part of the anti-sway architecture. Some have more than others and
has to do with the 'bend' in the bar/trunnion. The Blue Ox is an example of that
It may take a few cycles, as it is a guesstimation on how much tilt when unloaded