Ah, as you can guess, clearly I didn't actually play through that level. I can see now how annoying it can be.
But, I think one can argue that the given layout can be a sufficient and fair (but easily missed) hint. Basically, if you assume that all the steel plates making up the "frame" of the box should be the same size and not overlapping each other, then #1 does seem to be the only place that is consistent with such a set up and having a gap of no-steel there, with the tiny bit of black pixel implying that you got the top edge of a steel plate there. That in turn forces #2 and #3 to have fully steel behind the snow (otherwise either you have different-sized steel plates, overlapping ones, or weirdly shaped ones with ireegular edges and/or holes).
So maybe not too unfair, but sure, I would rather they spend their cleverness in other ways.