Co-location and Osmotic Communication

We all know that Agile and its various flavors (Scrum, XP, etc) place huge emphasis on face to face (F2F) communication. In fact, this is one of the key principles of the Agile Manifesto.

The most efficient and effective method of conveying information to and within a development team is face-to-face conversation.

For F2F communication to be effective, it is absolutely necessary that the delivery team is co-located.

Which among the below would qualify for a co-located team?

1. Team members seated in various offices in the same city
2. Team members seated in different floors of the same building
3. Team members on the same floor with Dev in one zone and QA in the other
4. The entire team seated in a room or within a single bus (the one that we travel in) length.

While all the above fare much better in comparison with a team that is split across different time zones,