I really like the way you make the premises concrete - "the borderlands are just visible from the porch" is pure gaming fuel.
In my White Sandbox I have the premise that dungeons are typically in 10' increments and oriented N/S/E/W because this is how the ley lines run. Trying to excavate against this cosmic grain is more difficult, and a dungeon like Blackmoor's where everything is askew is not just a mapping annoyance but a source of horror to the pious and evidence of having been built in a more chaotic era of creation to scholars. However I don't do nearly as much with that premise except for minor cosmetic things like saying that holy symbols are right crosses 10" long that function as compasses; you've taken a similar idea much further.