Think about a ported speaker box. Too big of box = no port velocity = no spl. Piston is the speaker, crankcase is the box, transfers are the port. There is an optimum case size for a given bore size, and transfer size. To big of crankcase would lose you some velocity even given how air flows from high to low pressure. If someone actually set down and did some calculations, I think one could tune the case to the transfer ports.