Originally Posted by EldRick
It didn't work because you had already opened that book with the previous settings. The line-height setting is retained for each book.
Changing the value in the configuration file only changes the default that will be used when you open a new book.
That isn't quite correct. The per book settings are only stored in the database if you open the font settings and make a change. Once you do that, whenever you open that book, it will open with those settings. Those settings are written to the configuration file and used as the default for other books.