I'm not criticizing 3D...it's not for me. I know where the vitals are on the animals I hunt and where to aim. 3D deer targets set at different angles and yardages help the bowhunter learn where to aim under that situation.
As a ground hunter, my methods are more efficient. I shoot from all angles, kneeling, uphill, downhill always selecting that small target to challenge me. I don't bowhunt from tree stands...not sure how many tree stands are set up on the 3D courses.
Take 4-5 small 6" foam squares and place them at random distances in your back yard Randy...Now spend a few days shooting at them. You will find you need to concentrate more on hitting those smaller targets BUT your groups will tighten. This should carry over to your Deer target shooting. You will be concentrating more at a smaller area where the vitals are located
Again...nothing wrong with shooting at deer targets....