.... Most cradles have a gap betwen the attachments but why can't
both lines be at the very top?

Doesn't the gap serve to stop the balls rotating about the vertical
axis? There's no way my addled brain can model such things these days
but I think such spin would be a "bad thing" - unless you are also
trying to demonstrate snooker shots
--
Robin
PM may be sent to rbw0{at}hotmail{dot}com