Thanks for the replies.

I'd tried adjusting the thickness, on the ncloth, but missed doing it on the passive collider. I've changed that too now and its sorted out the floating problem. However the table now penetrates through the cloth at the corners.

The cloth still looks very rounded at the corners. I'm sure I've got enough edges, as I've tried increasing them until my computer can barely run the animation!

I think I'm just going to take the deformed shape and tweak it manually to what I want, but I'd be interested to hear if anyone has any further tips on sorting out these types of problems just for future reference.

Thanks again.
Frank