[GeoffR]

Try adding line-height to the list of other CSS properties in the filter list.

But this is a brute force solution, and might have some undesirable consequences (for example multi-line titles and headings in large font sizes may overlap). A better solution, if you are not satisfied with the results, is to edit the .css stylesheet manually, removing line-height lines only from the classes used to display the main text, but leaving those lines in place (or adding them in with a moderate line height of say 1.2em if not present) to classes used for headings etc.

Edit: If you don't want to edit the .css manually you could also try adding h1,h2,h3,h4 {line-height:1.2} to the Extra CSS (CSS supplementaire) list. But this will not work if the publisher has done something stupid like using p instead of h1,h2, etc. for headings.