I have a question more out of curiosity than from trying to 'break' the game, but is there anything in the rules that prevents a model from going through a gap where their S's hight is not fitting? like a crate stacked over a couple crates with a gap between those two. I've only found that there should be enough space for the model's base to fit in. So basicaly I'm asking if I am missing something from the rules that would prevent model from crouching movement under something like a partial low celling. My guess would be, based on FAQ about base to base contact and stairs, that the whole S should be considered the base of a model for this case, but I'm interested to know what other people think about this.
You have it right, all the S need to have space to pass through. OTOH a Prone model has the height and wideness of his base...
If there's spaces on the board where you think a human-sized model should be able to squeeze through (bunch of crates leaving a 0,5"wide x 2"high gap as an opening between them, for instance), you should probably consider defining that gap as a Narrow width access point