Just a minor thing, but I think you are misinterpreting what I meant, in the example on the plains, The bridge four soldiers were outside the room (on the plateau) when shallan activated it, ergo, not within the fabrial, hence them being left behind when she returned to urithiru. What I'm suggesting is that it works similarly to how multiple cognitive entities can come to view themselves as a singular entity, The fabrial 'knows' what is part of it, and what is not, So the room itself is transported but anything outside of the confines of the room (like the rest of said plateau - and the bridge four members) stays put. Let me know what you think.
ps. Please excuse any spelling errors or non capitalisation, I'm on my phone.