@Morsealworth: Lucky you, then. The US is a hellhole, but--on the other hand--the US isn't the only place with cities like the aforementioned. Such places are all over the West.
That aside, your claim to "struggle" is disingenuous, but I'll humor you anyway: regarding pelvic shape, such a thing is most clear when someone is disrobed; the more clothing one has, the easier it is to hide that difference between the sexes. This goes double for the "small, well shaped breasts" (oxymoron if I ever heard one) you speak of--which are also a clear sign of the disingenuity I accuse you of exhibiting: Assuming Krusche is indeed female (almost certainly is, we know how this sort of thing goes), she has a bust that's so small, it barely distorts her upper garment in a way that's distinctively feminine; there's so much evenly barren real estate below her collarbone that, anatomically speaking, whatever swell has been shown as of late to stimulate the wall-sucking closet-dwellers isn't properly placed on her body. Indeed, you can see the artist stop trying at page 18, where Krusche is depicted as being completely wall-flat. Drawn accurately or not, it's a simple matter to hide breasts that are so
undeveloped: wear the bust-suppressing chest bindings that are used to effect this same trap song-and-dance that's been seen throughout anime/manga history, from well before Hundred to now. Assuming Infinite Stratos didn't take the chest-binding route, then sufficiently loose and/or thick clothing would suffice--which is likely the case for Krusche, here. Only problem is that the author is bait-and-switching by repeatedly (but not always) throwing Krusche's butt in the reader's face while stuffing the romantically-involved MC into the closet by depicting his lust for a (heretofore depicted) male.
All that said, if Krusche's design wasn't made with
androgyny in mind--if it was really as difficult for someone who looks like Krusche to pass as male as you say--there wouldn't be three pages of the aforementioned wall-suckers blowing their heads (in one way or another) over him.