Originally Posted by davidfor
If you want to use one of the missing size, you can edit the "Kobo eReader.conf". This is in ".kobo/Kobo". Find the line with "readingFontSize" and change the number. If the size you want is in one of the gaps, then the device will use it as the default size. If you change the settings on the device, it will update the file and lose the size.
I don't suppose you know how to get the .conf file to show all the possibilities, and not just the setting for the current book? I've tried going to Home and restarting and a simple paperclip reset, but I'm still just seeing readingFontSize=24.
(Turns out 23 is my sweet spot. How annoying!)