a difference is the distance from the center of the disc to the edge where the calipers make contact. Larger distance, meaning bigger discs, can impart more braking force to the hub or axle if all other parts of the equation (e.g. clamping force by discs) are equal.
So no, I don't think it really matters where the calipers are located along the circumference of a disc. Someone else might have a different idea.