Going forward, you are limited by the steering wheel cut, not the bed length. Almost all cars and light trucks have a steering wheel cut of about 35-37 degrees. With a 90 degree turn, the maximum angle between the truck and fiver will be in the range of 45 degrees.
I've used short beds for 25 years and never had contact. Started before sliding hitches existed and did fine for 14 years. Then 11 years with a manual slider that I never used. Recently switched back to the fixed legs. With the notched front caps on today's fivers, there is almost no need for a slider. What I learned long ago is that most tight maneuvers can be solved with a little more jockeying back and forth. I did have one of those situations, tried several times w/o using the slider, then nothing better with the slider, finally went back to the towing position and completed the maneuver.
Or you can get an 8ft bed or an auto slider or the Sidewinder and have no worries, but you still have to pay attention while backing, jack-knife past 90 degrees and there will still be truck to fiver contact. Finally, sharper angles result in more stress on the fiver suspension and tires. I wonder how many blow-outs are related to earlier stress on the tires. BTW, that short bed with a flat front fiver will still jack-knife sharper than is possible with any TT setup.