Hmm;
I wonder what effect would be observed if you were sitting on one of the atoms ?
I guess you could say that the outsides of the box might be the thing that's contracting (not you, & your atom vehicle), and you'd measure an increase in pressure, also. The box could be perceived as thing that's squashing you and the surrounding atoms. This would depend on the size and mass difference between you & your atom, and the box, I guess.
There's also some words on this in the
next paragraph in Wiki.
Cheers