Not sure what the cause of the issue is.
Some things to consider -
Focus system alignment, or rather, misalignment, would not give you front focusing on all the peripheral points. That is, misalignment, with a good center, would give a combination of front and back focusing.
De-centering usually gives one edge focused, the other edge not.
Curvature of field is an interesting issue. Not sure if most folks fully realize that film cameras do not hold the film flat. Film itself has a curvature, and various means were used, beyond a simple pressure plate, to try to hold it flat. I did extensive testing in the latter part of the 1970's with Nikon F2 cameras and film flatness. In those cameras, when the pressure plate was upon negative film, the center of the film was about .0025 removed from the plate. The film touched the plate about 1/3 out toward the edges, then gradually sloped away from the plate again toward the extreme edges. The shape was sort of a M shape (or W). It was assumed that camera lens manufacturers left some residual curvature of field intact, in order to actually improve imaging. I was able to observe that curvature when setting up the focusing systems in those cameras (a real pain in the butt and then some!), which were adjustable in almost ever imaginable way to assure near 100 percent coverage, and perfect focus on any area of the screen (or as perfect as film/lens combinations would allow).
What I'm saying is... knowing film IS NOT flat, and that sensors ARE flat... makes for interesting relationships in hardware.
