Mostly has to do with how you plan on gripping the bow. If you like to use a full hand or low wrist then keep your handle close to center between the nocks. If you like to use a high or straight wrist grip then shift your handle lower down the bow or toward the lower nock. Example: (assuming a 4" grip here)full hand/low wrist-keep handle centered. Measure up 2" and then down 4" for your handle. High/straight wrist measure up from center, say, 1" and then down 4" for the handle. For a medium grip somewhere in between.
Everyone's different on what they like so just experiment and see what you like. But always keep your center marked during lay-out and adjust from there. When your bow is complete you should be able to balance it on your finger dead center of the bow. If this doesn't happen then you will have to grip the bows using a slightly different grip then intended.
ART B