[flusteredBias]

This is anecdotal and I hope someone who has some research experience can say whether this is true or not generally, but I recently got a Kindle and found that if I use really large font sizes where there are fewer than 50 words on a page it's easier for me to stay engaged. Maybe this has something to do with cognitive load or chunking information. Some fonts look quite a bit better at these large sizes. So for me I don't think typography alone is sufficient. I think the interaction between a large font size and a typography that looks pleasing at a large font size helps with engagement.

[hajile]

I knew someone who would with an opaque ruler with a hole on one end. They would read the words through the hole and I guess it helped them stay focused on just the word or two they were reading. It sounds somewhat similar to what you are describing.

[WillAdams]

The normal standard for line length is 2--3 alphabets worth of text.

I find that shorter ones break up and slow down my reading, while too-long lines make reading wearisome to the point where I actually bought the Kindle version of:

https://www.goodreads.com/book/show/37858510-the-inklings-an...

to read rather than the print edition.

[JKCalhoun]

At the same time, don't all fonts, typographically, look better larger?

I don't know what the DPI of the Kindle display is. But since you called it out specifically, perhaps the issue you are having is more specific to that device. Contrast with how you perceive reading on a high-DPI laptop display perhaps.

[browningstreet]

When I've done that I feel like I'm reading a text message, not a book (fiction or non-fiction). Possibly not a universal experience.