WYSIWYG is rather "pointless" overall for ePub, because unless you have an emulator for each and every device you're planning to have viewing the ePub file you'll never be guaranteed of the "perfect rendering".
You have to rather "let go" of the desire to control things at the pixel level else you will go mad. It's something a lot of web-designers really lost a lot of hair over (and still do). I guess that's in part why I like things like
LyX a lot, because it forces you to let go. So long as you're stylistically consistent should come out quite okay (and if not, then a few CSS tweaks should fix it).
Paul.