I don't recall ever seeing such a setting. I was under the impression that the margins, line height, font size, and so forth can change for each book if the book sets them in the css. Which is why I go through the trouble of editing each book setting the css to something "default";
Code:
body {
font-size: 100%;
border: 0;
margin: 0;
padding: 0;
width: auto;
}
I also do a search and replace on the css beforehand and remove all line-height and text-align settings for left and justified (leaving center and right alone). It's not quite that simple because paragraphs and spans can have a class changing the font size so I remove those classes in the html.
After that the reading settings in the kobo are consistent across books edited thusly. It may not look pretty but at least it's consistent across books.
But I was mistakenly under the impression that the kobo's setting for ragged right didn't work if the css specified justified, so I could be wrong about all of this as well.