Sorry for the delay in replying.
The CSS code looks good at that point and is exactly as above. This seems to kick in for iPhones no problem.
iPads however, seem to think they are something special!
I’m afraid that did not work. It seems that issue is specific to iOS on mobile devices – according to some people the problem is that iOS is using the full height & width of the body instead of the viewport to decide the size. See: https://stackoverflow.com/questions/24154666/background-size-cover-not-working-on-ios
Unfortunately for us, most tablets seem to be iOS devices!