TC, in a comment in my last post made several observations, which you can read HERE.
But he also reminded me of the textual problem in Ephesians 1.1 regarding the recipients of the letter. The fact that this construction is so very rare and consistently is used to denote where something is. It seems highly unlikely that the words ἐν Ἐφέσῳ are not original to the text of Ephesians.
The only explanation that makes sense of the words not being original with this understanding of the syntax is that Paul left a blank to be filled in on arrival at the letters various locations.