Thanks for that information. It sounds logical.
However, it begs the question: Why wasn't a simple pintle mounted MG fitted, with or without a shield, as on mid to late war StuG IIIs?
A shortage of remotely controlled mounts explains the absence of such, but I still find the lack of any sort of all-round defence surprising. I suppose other German Jagdpanzers had similar deficiencies though; for example the Elefant/Ferdinand still mounting only a hull MG even after post-Kursk modification. Also the Jagdtiger and Brummbar.
Incidentally, I'd really like to see a picture of the internal mount for the MG used in the Jagdpanzer IV, and the method of operation of the armoured port. Detailed photos of ball mounts seem to be easy to find, but I've never seen one of the manually opened MG port on either the Jagdpanzer IV or Panther Ausf. D.