As a textbook author, have you ever asked your students how they read your book? An inquiry into how your students read their textbooks may reveal much information that can help authors design textbooks with students in mind.
I recall when I was a college student―yes, a very long time ago―how I read a textbook chapter for a college course: I set aside at least 3 hours of undistracted time, read the entire chapter word-for-word, took copious notes, spent time examining and understanding all of the figures, and then systematically answered every single end-of-chapter question. Only after this procedure did I feel like I had a good understanding of the material.