DaveInNYC: Keep in mind that Eliezer still has yet to get to "wave function collapse" or "find[ing] a particle at a certain point". That's the "magic wand" that "detects a ratio of squared moduli of amplitudes".

He hasn't given you that tool yet, so if you're just following his posts so far, you can't even ask the question that you want to ask. So far, there is no way to "observe a particle" in any particular place. There are only (spread-out) amplitude modulations.

That may not be satisfying, but I suspect the only answer (here) at this point is, "wait until a later post".