Have you tried adjusting the Space Before/After factors for these styles?
Note that each style has both a before and after "factor", and these combine with (get added to) the corresponding values of the styles above and below the style in question. Another complication is that the text itself gets locked to the grid, so the values you enter here won't always produce the results you expect due to the grid.
You may want to also experiment with a new feature (2.6 or later) allowing the text to go off the grid:
This allows more control over the spacing, but has other interesting effects - and is only recommended for DRAFT printouts and short runs on thicker paper. Avoid using this feature for thin Bible paper and large production runs.