at / in the office

I quite agree with JackInMadrid. The more I learn about prepositions at/in, the more I’m convinced about the fact that at indicates the location and indicates a place to meet, generally at the

door

of a place (at the office, at the library, at home…) or in any other cases a

reference

, a

location point

. For example, I wouldn’t say I’m meeting him in the square but at the square (square being a meeting point). In the other hand, in indicates an inside location where the speakers is. Generally open or enclosed space referring that you’re somewhere beyond the entrance door or within an open area. I’m in the square meaning you’re inside it. Which means that you’re probably saying this to someone on the phone.
If I’m on the phone in my office, I would say, meet me in the office.
If I’m on the phone outside the office, I would say, meet me at me office.
Which is more or less corroborating what you said in your example.
However, about your last example, in my opinion, if you are out of the office and you say is John in the office, I would interpret it as being somewhere in the office whereas I wouldn’t say he is at the office for the same reason that in my mind at indicates that he is at the door or he has just arrived at the office.
My conclusion would be that at would be used where you want to do something at a place (meet, have a party, etc…..). Whereas in is more likely indicating where somebody is. But please, tell me if I’m wrong.

I would be grateful for any comments on this from anyone.
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