@Joel
I checked the source code of the book before with sigil.
All the book text is inside the p element.
I tried it even with a new book, where I never made settings at all.
The "Kobo ereader.conf" saves the last manually edited reading settings. Before I uploaded the new book, I checked the "kobo ereader.conf".
It has the entry "readingLineHeight=2.5".
When I open the new book it gets the lineheight 2.5.
In other words:
There's no way to absolutly control the appearance of new Kepubs.
When you (accidentally) edited the reading options on any other book before, the new book takes these values.
Further:
There's no way to reset the reading options "to the default css of the book".
Like it is in an internet browser.
