Overnight it clicked that "the construct" is Stephan's camera image quadrant where he is using (subject) reflectance to define the x axis scale.
The thing that was new in concept to me was that on a standard H&D curve, image compression on the straight line of the curve is possible. I had thought that the H&D curve was a better visual representation of what was happening in the image in real life than it really is.
Seeing the curve tied to the subject mater in the camera image quadrant gives me a much more relevent representation of what's happening to my print. Like the negative itself, the film's curve shape is only important as a reference guide to a storage device, a map of where it is holding the info about certain tones.