I had come up with the same answers, but using logic from a different direction.
Figured a longer focal length would produce a bigger arc. That arc would be the plane of good focus. With the bigger arc, no part of the building would be as far from that plane of good focus as they would with a smaller arc, so the bowing would be lessened, and the image would appear to be flattened a bit.
I'm guessing that terms exist in this world for the concepts I'm describing, but I don't know the terms yet.