DIX is also called Philadelphia. While I'm not a big fan of Philadelphia I do think it's a "big" region, both in population and physical size. There i also a mjor NWS office in Mount Holly, about ten miles from DIX which, to my mind at least, adds some importance to DIX. That said, I can understand having some granularity missing for simplicity, but given that DIX/Philadelphia covers , basically from NYC to Baltimore I would think it belongs there.
If I click on Binghampton or Staunton, the two that appear, location dependent, on NJ in the map, I can get to DIX/Philadelphia from there so it is, indeed available.