Well, I've done downstairs twice and upstairs once so far, and each time the box was full to the corners. So maybe if you live in a rat infested pigsty like my house, the debris will work its way into all areas of the box as necessary. If you instead live in a nice tidy place like yours, maybe the debris collects around the inlet, as there's not enough smeg to push it outwards?Interesting, as on mine it certainly collects the dust around the inlet as that review described. However, my floors are pretty damn clean in general so I think maybe you just had more debris laying around. When your Mi does it's job on a regular basis and the dirt/dust levels in our place stabilize then I would guess that you will also find that your box is pretty light on debris at the end.
Amazing piece of kit though.
Point being - Maybe you need to get some rats and pigs in?