Like yourself, I am having great benifit from the course with nonfiction.
My biggest problem with PR in the beginning was I was using a book that was 90% story and 10% meat and I just couldn't do anything with it. NOW I could do it, but not back then.
Nonfiction usually doesn't have a story line, just a bunch of facts.
Dana once said for novels he PR's then RapidReads. I PR then slow read but speed up over non important parts. You might ask what's the use of PR if you have to slow read anyway, the PR is like a subconscious preview. The only way you'll see what happens is to read 10 novels and only PR 5 of them before you read it. The ones you PR, you'll have an understanding as you read and I think you get more out of hidden meanings in the story.