Investigate the Sliding feature. This is located on the Inspector, Position tab, near the bottom:
If you choose "Sliding up based on" and "All objects above", then any blank space in the field / object will be removed when the layout is previewed or printed. "Also resize enclosing part" will cause the enclosing part (in this case, the Body) to shrink vertically to close up the empty space.
Many thanks, Mike. I thought I'd tried that, but obviously not.
I need to do some fiddling about with top and bottom margins but I think the basic problem is solved. Thanks again.