I’m glad that makes sense. One other thing to check….when you say your lens is sharpest at f6.3, is that in the center or across the entire image field? I ask because many lenses will be tack-sharp in the middle, but soft around the edges. For a normal photograph or portrait where the subject is often near the center or at least at the 1/3 it’s fine, but for camera scanning you want the best possible sharpness across the entire image.
That’s another example of a setting you want to get right up front before you camera scan 10,000 photos. 🙂