Her head is above the top tube in the space above it.

I suspect the metal sheet rolls or folds so that it doesn't actually bisect the box.

It's a cool trick, though. The set up is great with it looking like the girl is facing the door of the box and you assume she stays that way. But I fell pretty confident she turns sideways, back against a wall, stomach over top tube, legs stradling bottom tube, sheet folded or rolled up along slot it goes into.