The angle of the head means very little or nothing in terms of the amount of force developed by the bars with the bars under the same amount of pre-load (ie, lifted the same distance by the brackets). The angle of the head is mostly used to simply set the height of the bars along side the trailer frame rails. I mostly set the angle to have the bars horizontal when snapped up into place.
I am with the Materials Engineer. Looks like a simple brittle fracture to me. I always thought those drawbars were forged, not cast, but obviously I was wrong. I had one for a long time, I always used the inner hole to make the stick-out as short as possible. Now I have the solid steel and welded type. If in backing into the driveway you have to transition to a typical slope upwards you would have put the highest stress on the drawbar that you saw on that trip, so it's understandable that it broke at that point. Only possible good news is that those types of failures are often "infant mortality", they happen right away or they don't happen at all.
Sorry to see that. I used to believe that Reese et al was the creme de la creme of the hitch world, now I buy from whoever is cheap at the dealer or Tractor Supply Co.
Brian