OK, after doing some tests it seems the editor gets its display settings by default from the BODY class element.

Is there any way to tell the editor to get its default style from somewhere else?

I guess what I'm trying to accomplish is for the editor to display what will be shown on the page.  If a user explicitly applies no styles then it will pick up the default (containing) style - which in DNN is NORMAL.  Is there a way for the editor to work out the default containing style?