I don't understand how being in that combo would reduce the chance for a mis-shift (or why you would be concerned about a mis-shift if your drivetrain is properly adjusted).

Being in the middle of the cassette offers more shifting flexibility, especially quicker shifts into easier gears when compared to being cross-chained. I can't think of any advantage to cross-chaining, other than having to run a longer chain which will give you more chain slap.

I've read the book a few times. I don't know of any movie adaptation.