My passenger mirror was dealer installed. Not sure if there were any dealer notes on the placement or if they just put it where it worked best. Surely they had to have something to go by as I am betting they did not want to have mirrors installed where the buyers could not use them and then have to re-install them and fill in the holes they just drilled into someone's brand new Camaro.
When I first noticed the difference, I thought that whoever installed the mirror did so with no thought as to what was proper and just screwed it in wherever. However, if you place the mirror in the exact location as the driver side, the mirror has to come in too far and doesn't really give a good viewing angle. However, when screwed in where the original holes are, the angle is just about perfect and the mirror is centered very nicely where you have an almost equal adjustment distance up/down and side to side.
My driver mirror is about 3" from the door edge and the passenger mirror if about 5-1/2" from the door edge. That works great for me. If anyone wants photos or measurements on the placement of my mirror, I will be happy to send them to you.