My position is that most of the questions should stay on Physics.SE, with some exceptions. I mean "most of the questions" to include those which are:
Not about the creative aspects of astrophotography (composition, background, post-procesing effects, etc.).
About aspects of astrophotography that do not have a large number of experts on photo.SE such as noise, photometry, image processing for the purpose of measurement rather than aesthetics, imaging outside the visible spectrum, diffraction, etc. (eg. most photography experts wouldn't know what was meant by "H-alpha" and if they do they are probably also on physics.SE)
Asked in such a way as to imply that the desired answers should come from a technical/scientific point of view.
The rest of the questions, those which are clearly about the artistic aspects of astrophotography and obviously off topic on physics.SE, should of course be migrated.
However, when there is doubt about a question being on-topic at physics.SE, but it is not clearly off-topic, we must consider that it was originally posted at a technical Stackexchange and the asker presumably wants a technical response. When it does not violate the physics FAQ to do so, we should attempt to respect this decision and leave it on physics.SE. In my experience, the photo.SE community is uninterested or even actively opposed to answers which are technically and scientifically accurate, in favor of more conceptual "rules of thumb" which may be helpful to photographers, but incorrect in a technical sense. This is not a knock on the photo.SE community, but it does mean that we are being inconsiderate of the intent of the question if we move technical questions from astro.SE to photo.SE.