Well, Kobo is very respectful of css in Epub, in line-height for example.
You can change css (and if the book is from project gutemberg You can do it without problems, eliminate line-height property for paragraph) or You can apply patch to change that behavior so You can change line-height as You wish in each book.
https://www.mobileread.com/forums/sh...d.php?t=260100
https://www.mobileread.com/forums/sh...34&postcount=9