Once I have seen the diagrams. This gamma distribution seems to be a quantum effect via sensitizer or dyes, depending on this, it can be minimized, when pictorial necessary, or enhance. Any minimal discontinuity (like low contrast resolution parts - the grain from a photographic wedge scale) interrupt this quantum effect.
When you look at the uneven development of negatives, special looking at the borders near the perforation:
1. Not enough movement is only a part of the truth
2. an equal great part (maximal the whole 24x36mm negative) has boarders with higher densities thanks the quantum-effect, when it is not chemically cancelled.
A friend told me today: When you enhance the quality of a paper (and you use not modern high resolution films with minimized grain), the (low contrast) grain becomes more visible. Enlargements from normal mix-emulsion grained 6x6 negatives to 8x10inch paper will -on thuch paper- suddenly looks more grainy. This happens in around ? 1984-88 ? with Kodak Polycontrast 3 from this production date. Later produced paper with that name had showned normal qualities.