I can assure you it comes as no surprise to anyone that a bigger box can carry more stuff than a somewhat smaller box. But you might also see from the this relationship that this somewhat smaller box can carry more stuff yet than an even smaller one. Given some experience with boxes, you would become aware that their utility function does not scale linearly with size, which is why most of the public is fine with a sedan, therefore somewhat more with that somewhat larger box in a wagon which was the case before they became unfashionable in the US, and so on.