different layers at different distances from the camera (yet moving at the same speed) appear to move at different speeds when viewed with a perspective camera. This effect will not work with an orthographic camera.
different layers are intentionally moved at different speeds to fake the parallax. This is necessary for orthographic camera setups.
Rather than links to text solutions, perhaps a pointed time-stamped video of a game that uses this particular effect would help nail down what you’re trying to do?