Physics is concerned with an understanding of the Universe, and is an empirical or experimental science. Physics is therefore concerned with truths about the world which may be discovered by observation.
Metaphysics is concerned with a philosophical understanding of the world as distinct from a scientific understanding. This may be a kind of understanding which is prerequisite to empirical enquiry, or it may represent a perspective on the kinds of results which the physicist might of obtain, perhaps taking the view that things are not as they appear to empirical science.
The metaphysical position we adopt is engineered to provide a philosophical account consistent with the view of science as constructing conceptual or mathematical models of the world which are judged (in part) by their predictive capabilities.
Any finite set of observations will be consistent with the predictions obtained from a variety of mathematical models. Even if a model is known to be perfectly consistent with all the experimental data it may therefore not unambiguously establish the structure of the world. We therefore take the position that the ultimate nature of reality is beyond our reach.
Metaphysics sits on the common boundary of the fundamental triple-dichotomy between analytic/synthetic, necessary/contingent and a priori/a posteriori knowledge.