I bought two of the Heyn Rad 0 circles (each of 8 x 45 degree sections) a couple of years back - one with the standard sleepers (which are visually close to "normal" Euro G) and one with his field-railway "rustic" sleepers.
I've laid it on the floor and tested it with a Stainz and a couple of four-wheel wagons, both Feldbahn shorties and LGB standard 4-wheelers (starter set coaches).
The Stainz handles the radius OK in both directions when running solo, and runs well both ways with the feldbahn short cars; with the standard-length four wheel cars it runs fine bunker-first, but when running smokebox-first it struggles a bit with coupler lock-up due to the excessive outswing of the cab end of the loco - it will manage it (just), but is not 100% happy.
One of the little Feldbahn locos with matching cars would be fine in both directions.
Jon.