In the example I posted, the edge effects control apparent sharpness. Due to the nature of emulsions and developers which can interact, edge effects can either cause lower or higher contrast as the size of an object decreases. As size decreases, one goes from the realm of macro contrast to micro contrast. Thus, you might take a picture of an object on 4x5 film and 35mm fim and make the image the same size in a print and have them appear different in contrast because the smaller image may have higher micro contrast.