When the interanl dialogue is about the book asking questions and that. then you're following your intentions. Consider that fine.
If you notice that your internal dialoge is distracting or mind wandering then you probably haven't got much from the book.
It's possible to go through the motions and be on another planet mentally and for sure you haven't PhotoRead the book. No great loss bring yourself back to a chant that reinforces your intention and PhotoRead again only takes 2 to 5 minutes for a book anyway. Many folks have experienced the fun of having their mind wander while reading 6 or 7 pages and come back saying now what on earth have I been reading this past 20 minutes.
Alex