"If there was any large ramp or embankment abutting the face of a pyramid there would be no reason to lay the casing stones from the center outwards. You would start from opposite the ramp, and finish the course at the ramp's upper end. The ramp would obscure the outer geometry of the pyramid on that side, and thus there would be no benefit to always laying the casing stones from the center.
But if each pyramid face is free and unobscured, then a center line can be established and the casing stones would be set extending from that position."