The only way a single double-acting cylinder will be selfstarting, is if it stops in the correct position(s) for starting, every time it is shut off.
Older Jensen 10´s are well known for doing so, when adjusted accordingly, as the magnets on the crankshaft mounted generator, will stop the rotation at the same spot(s) every time.
I never thought about that before Jan, but I know your correct (something to keep in my memory bank)