Yeah, but don't forget the Roche limit, defined as "the orbital distance at which a satellite with no tensile strength (a "liquid" satellite) will begin to be tidally torn apart by the body it is orbiting." In other words, if the center blocks were more densely packed (producing some kind of "core" I suppose) then some of the outer objects, depending on the strength of the field, wouldn't be able to stay solid. I'm not exactly sure how else this would affect the cube, but I think it factors in somewhere.