I think what Mark is trying for in his sketch is to sort of simplify the tone reproduction illustration by essentially fixing all the variables except negative exposure. Somehow that is all modeled and fixed into the horizontal lines so that you then move the paper curve up and down and the shift directly reflects the change in negative exposure without showing the transitions. I think.
My thought is that this is similar to combining the windmill with a Dorst for the transition between subject and negative. Jones and Dorst diagrams can of course be combined (there is an example in Henry).
Or I may be out in left field.
What I'd say is that I'm not moving the paper curve, its fixed in relation to the scene. The variable is strictly the negative. The negative doesn't define zones, its just a transfer medium.
Mark Barendt, Beaverton, OR
"We do not see things the way they are. We see things the way we are." Ana´s Nin