Add chapter names to header, but only above a certain level

This is LibreOffice Writer, v4.3.5.2, on a Mac, though I have no reason to believe that it would be any different on any other version.

I have a page header which contains two Chapter fields - one set to level 1 and the other set to level 2. The idea is: I want the first one to show only the main, top-level chapter titles, and the other one to show the subheadings, where they exist, but be blank otherwise. Unfortunately, it’s not working quite like that. The field that’s set to level 2 shows the level 2 chapter names where they are defined, but otherwise its shows the level 1 names. In other words, when I set the field to show level 2, it actually shows levels 1 and 2. I’ve tried this with other levels too, and it works the same - a Chapter field of level 6 shows all the levels 1-6.

So, is there a way to tell the field that it should only show names of the given level? Alternatively, is there any way to hide the field altogether if the level is below some set value?

Thanks in advance,