This topic brought to my mind an ancient reading and - yes, I found it! - at "Enlarging" - C.I. Jacobson and L.A. Mannheim, Focal Press, 22th ed, where they extensively cover correcting parallel lines with enlarger movements. Some clever equations show that real distortion can come into the scene if specific relationship among camera and enlarger lens focal lenght, angle of tilts and magnification are not considered. Perspective and proportion control can be thought as diferent subjects and precisely calculated to include even Scheimpflug's law.
Obviously, it's really quite, quite technical. Almost boring...