ORIGINAL: early in
From what I've read, to get center shot your arrow needs to follow the "path of force". To get this, you have to get a nocked arrow to align with your string and sight pin. Some rest adjustment might be necessary. (3/4" from riser) I think this is right.
Early in, the path of force that you are talking about is probably different at full draw than it is at rest. That is why you need to set 3rd and 4th axis on sights. The arrow in most cases does not leave the bow perfectly perpendicular to the shelf. If anyone finds a setup that does, let me know. I will buy one.
The "in" "out" method for setting up a sight proves this theory. TFOX gave me a website that talks about this for further understanding. Maybe he can post it here for you to read also.....