@tomnorthfilm it is an interesting thought and one that is often noted when talking about medium format.

I think at the end of the day, it's the way in which the bokeh in an image falls off

I don't know the physics or math of it, but, my hunch says it's because of the "flatter" DOF plane. On FF you can get shallow bokeh, but, that plane tends to become curved and warped or soft on the edges. With LF, you get the thin DOF perfectly flat across the image.