I grabbed one of my Kindle books, saved it as *.docx, and went through the whole thing in Word tagging Heading 1 and Heading 2. The book seemed to build OK: I do see all the headings I tagged in the left-side table of contents.
But when I make a reading plan, all those headings seem to be ignored.
How can I force headings (or whatever) that the reading plans will acknowledge?