window.placementTarget

A window linked into two sessions is one window with two placements sharing an id, and a bare @id leaves tmux to choose between them — which it does consistently, and consistently without regard for which placement the handle came from. Qualifying with the session is what makes an operation act on the placement it was reached through.

Only the operations that address a placement take this. kill , rename , selectLayout and resize act on the window itself, wherever it is linked, and naming a session there would suggest a choice that does not exist.