The eye naturally seeks center. As a rifle shooter using iron sights, this was made evident to me. Seeking center is also natural when shooting targets, that is where the bull is. Cork and double cork.
In the fleeting seconds before a shot, those natural tendencies are difficult to overcome. Mentally selecting a sector of the deer in which to then pick your spot is a discipline that needs to be developed in practice so that it can be utilized when the shot is presented. As your brain is usually a tad scrambled and running on blind conditioning at that point, practice is essential.
Rifle silhouette, which I took up to improve my shooting and give me the excuse to shoot more, did me a disservice in that I conditioned myself to aim for center of mass on the steel targets. Time my wobble, and snap the trigger as the crosshairs swung toward center. In the field, I went through a spell of "just a little far back."
I had to consciously untrain myself in order to get back into the groove.
Killdeer