Hmmm, taking note of this I thought I'd try my new Deltic, hardly run, with this in mind. I reversed her up to a Bachmann Mk.1 and drove her through the track system, which comprises express and medium points on track with radii of 24-30". Apart from one instance, initially, of a loco slipping her couplings, which was not repeated on a second pass-by. Reversing was not a problem, with the couplings on the coach sliding easily on the deltic's coupling. There was one small problem, I have a curved point which runs into double slip from a 30" radius track, which caused the loco to derail, without any effect on the coach. I presume my track geometry is not quite correct here!
In respect of the other points and junctions, I assume then the coaches' swivelling bogies enabled the couplings to work properly.
I then repeated the 'experiment' with Bachmann box vans, with standard couplings. No issues were to be had.
My track is far from perfect, but might best be described a w-i-p. The loco traversed a 24" radius curve on a very slightly rising incline as part of a triangle. No issues, much to my surprise.