I've added a new `Force user line spacing in KePubs` patch to post #2.
Some publishers create their books with every paragraph wrapped in <div><span> tags, instead of the more obvious <p> tags. This can prevent the line spacing set by the adjustment slider from taking effect.
This patch will force the line spacing set by the slider to take effect even on these problem books, but it might also override some line spacing that it shouldn't in other books.
(If you are sideloading kepubs then it is probably better to fix the books by editing the stylesheet in Calibre before sideloading, instead of relying on this patch.)