Mirrors

Could someone pls enlighten me as to the correct position of the offside (passenger side)external mirror. I was just going put it in the same place as the driver side (directly opposite though) when I noticed on my son's Ford ,there was a difference of about 4 inches, the passenger side set back - so as to afford the driver a clearer view ??? What was the factory placement on A bodies (68/69 Darts especially).A big shout to the Professor from Aussie Dart.