If someone imagines the 3-D space as “concrete in-itself”, it needs to be contained somewhere, as material things occupy an empty room. If you imagine such an empty space containing the current space exists, then we step into an infinite regress. Where is the container space contained in?
We need to assume that the whole structure of the material world is purely informational with no physical substrate. It is still concrete and governed by physical laws, but there is no concreteness in itself apart from relative concreteness.