I've read this thread and while it does seem to give me the answer I am looking for, I still wanted to ask a related question.
Let's take the following sentences as examples:
"He lives in a flat, and she lives in his same flat."
"He lives in a flat, and she lives in his flat."
"He lives in a flat, and she lives in the same flat."
Considering the aforementioned thread, it should be fine to have an adjective come after a possessive determiner ("same" coming after "his"), however this kind of sentence doesn't sound right to me. Sentences 2 and 3 do seem like grammatically correct alternatives, though I can't figure out why they are correct whilst the 1st sentence is not.
Could anyone tell me if this kind of structure (sentence 1) is fine or not, and explain why it is/isn't so?