This seems to be the issue I had. When I ordered mine, that notice was not there and I received a frame that had a semi angled crown, rather than a flat one as pictured and labeled on the site. They replaced it with a flat crowned version of the frame but I suppose it must have been the last one. I recommend going with the 400mm frame if you can fit on it, otherwise it may be worth giving them a call.
If need be you could always get shorter cranks to give you that little bit of room. Plus the longneck is for standup tricks so you shouldn’t be sitting on the seat much anyways