In my experience, if both eyes were looking through the crease, I'd be crossing my eyes a bit. Probably not the desired situation. Instead, imagine that you are looking at something beyond the book. Do your best to forget that the book is between your eyes and whatever you are "seeing." If you can relax and do this, your visual field opens up and you get the soft gaze that Michael talked about.
For instance, sit with your feet propped up on a coffee table and the book resting on your legs. Rather than looking at the pages, focus your eyes so that you are "looking" at the portion of your feet that are hidden behind the book.
Hope this helps.