Ok my disks DO float!!
I went on a mission and took the wheel off for a closer look. I unbolted the disk and laid it on a piece of glass and noticed straight away that the metal surrounding two of the bolt holes was ever so slightly bent, as a result holding the disk tight to the wheel!
After a little "persuasion" with a hammer and the flat surface on the back of my vice the disk mount is now perfectly straight as is the disk.
Everything perfectly straight and floating and working pretty damn well, and also less sponge on the lever
Please note I'm not recommending anyone take a hammer to a bent disk I did it in full knowledge that it wasn't the best idea and may have ended up having to buy a new one. On this occasion I think Lady Luck may have been looking over my shoulder!