[davidfor]

Originally Posted by digital punk

Hmm, I would have thought the text size effectively altered the line height automatically?

You are right of course that you would get the best results tweaking each one individually. I was hoping to come up with a general protocol to save time and which won't cause any additional problems.

What you have is a reasonable first cut for the changes, but as GeoffR said, there are some other things you need to consider. About the only thing you can do is experiment.

I can't help thinking that this should be the job of Kobo to set their readers up to automatically anticipate formatting issues. I expect though that if I complain to Kobo they are just going to tell me to buy books directly from their own Kobo store.

Kobo actually does a good job of rendering the book the way it is intended by the creator. Unfortunately, this means some loss of adjustment by the end user. But, a well coded book will do both, show the styling the designer wants and allow overriding things like font size and spacing. But, automatically anticipating this means that Kobo have to code for any code put into a book. That's just not possible.

Originally Posted by digital punk

Also regarding a book with multiple fonts - it seems to me that the reader is at best just approximating the fonts anyway, probably wouldn't look the way the publisher intended anyhow, so not really compromising too much by using only one font.

Again, Kobo handles fonts well, but with one proviso: the font has to be correctly named. You can sideload fonts or have them embedded in the epub. And the device will use them and, depending on the font, display them fairly well. But, Kobo is strict about the naming standard for the font files and if the don't match what is expected, they will not be used.