You are pardoned.
I'm just teasing you, I don't think it's an issue of being dense, I think the wall formats are complicated things that were never explained by CocoaSpud.
The offsets are applied to the coords, while the wall_rect is that particular wall part in the graphics file.
As for 5 or 7 distant walls, that is up to the person at time of creation of the format. You can easily have both for the same wall format by changing the size of one of the graphics, so DC knows which to apply to what. For example, if the new wall format is 5 distant walls and measures 400x800, to use 7 distant walls, you would need to change one of the dimensions to say, 416x800. (Keep each dimension a factor of 16 to avoid issues with the editor.)
Edited to add: Check out
this thread to get some good visual guides for how walls work in the viewport.