If one enters tombs and catacombs and so forth in Alexandria from the Greco-Roman period, one is immediately struck by the mix of forms from all over the Mediterranean and Middle East. Mixing and matching of favorite Greek, Roman and Egyptian gods is very common. The Library of Alexandria was where every known book in the known world was gathered.
One would expect that an original to the Book of Abraham containing Abraham's own words in an ancient tongue would be found among the writings in the Library of Alexandria. Furthermore, among all these writings, one would expect the Book of the Dead and the Book of Breathings or Fellowship to have been found there too. It is in the Library of Alexandria where priests and scribes of many different traditions would have come together. It is in this place where the writings of the Jews would have been known, not to mention the fact that so many Jews were in Egypt to begin with. It is in this place where these priests would have had access to a rare book such as the Book of Abraham, where it could have been discovered by Egyptian Priests, who took an interest in its mysterious contents.
And since they had taken upon them this Syncretist notion of using Egyptian iconography for representationalism for things that had originated in other traditions, one would think it would have happened in a place where they had access to all the writings of the known world: Alexandria.
I believe it was in Alexandria where the notion was born to use the symbols of the Sensen Papyrus to represent Abrahamic themes. It is to Alexandrian Egyptians, it would seem, that we owe our debt for the mixing and merging of forms, and the association of the Sensen Papyrus symbols and those of the Hypocephalus with the text of the Book of Abraham. Whether they were ethnic Egyptians is another question. Ethnically, they could have been Egyptian, Jewish, or whatever. They were Egyptians because they were in Egypt, possibly in Alexandria. And they were perhaps, undoubtedly familiar with Gnostic traditions, both Pagan and Jewish, and the influences and ingredients behind Greek Magical Papyri tradition, if not entirely responsible for them.