I have done this with a "modern" truck. Following along in the truck alongside while the chopper clips the field and the blower blows it up the chute and into the truck.
There is a fair amount of play both side to side and front to back. And a lot of "forgiveness." The man in the tractor will tell you if you don't follow appropriately - don't want to overfill to one side or one end.
I worked for the power utilities for 35 years before being laid off in "deregulation" and finding my career path changed. I was never EVER thanked for my work at the utility. The farm was ALWAYS thankful for my help, and quick to tell me so.
I don't imagine "driving truck" has changed much to my experience. Maybe faster today?
Joe K