Michael S, sorry from coming by so late.
Regarding your fear and backing up when you superread. Fear is a nasty thing. If you don't have an easy method to reduce or elliminate it consider looking into it. They are not necessary for PR to work, but a good general tools/skills to have. I'll share some ideas about PR that may help you.
I superread just like you, but without the finger. I don't even try to consciously read. I'll notice words and thoughts, however my main objective is to see everyword and notice queues for dipping. When I dip I push my reading speed to minimize subvocalization. I'm dipping for information not the ability to quote.
As for noticing that you field of awareness sometimes narrows, I would interpret any such behaviour on my part as internal guidance. Afterall, I've already read the book and something like your narrowing vision is a way for my other than conscious mind to direct my efforts towards my goal. It would say to me, that there is nothing here I need to notice. Therefore I would definitely not contradict my inner mind and repeat the material.
As for the process of noticing that you field of awareness has narrowed, I would take that as a message that you should widen it and get because something relevant to your purpose is coming along.
I'll recommend try trusting your inner minds guidance, and making your conscious mind more of an observer. Never second guess anything you are doing. Never doubt that you are receiving exactly the guidance that you need right this instantance. Be quiet and notice and you will be lead correctly. Don't argue with your guide.
You are perfection.
Iam2 