I suggest you try ChareInk6SP NoWeight. It's a newer version of ChareInk and it has a smaller space. It works really well on a Kobo for both ePub and KePub.
Also, if you are using hyphenation and you want to make it work better, I suggest you download the better hyphenation dictionary from
https://www.mobileread.com/forums/sh...d.php?t=252405.