Oh. Well, I guess that's being a bit technical about it, I never really measures my angle of approach, but I'd guess it was often around 45°. The better way of saying it is: If you have very little overhang, you're good approaching it at an angle, but if you have a LOT of overhang, you're gonna need to straighten the trailer BEFORE you slip it into the hole, and therefore will need a wide aisle to do it in.
I know you said you didn't want any links to videos, but this guys YouTube channel is professionally done and it's almost 100% devoted to backing techniques. He's even created a computer truck backing simulator that you can buy for $10. Other than that, it's just kind of fun to watch. Drivers from all over the country send him information on their toughest backs, and then he works out how to accomplish them. And believe me, some of these locations are truly wild. 'My Trucking Skills' channel