joot: I cant draw you a diagram of this but if you have a multi-pin sight (say 5 pins) and they are set at 20, 30, 40, 50 & 60 yds - these pins are in a vertical line. If you are shooting at 20 yds you of course use your 20 yd pin placed about 1/3 up the body. Your 30 - 60 yard pins, for a quick check, should line up the rear edge of the front leg.
So what you have is your 20 yd pin properly positioned for height and, with the rest of your pins lined up behind the front leg, which will ensure you're not going to hit too far forward or back.
Now this applies only to a broadside animal. For a quartering away shot, you would align using the opposite side leg.
IMO the best image I can give you is to picture a soccer ball set between the animals shoulders. You visually divide the ball into 2 halves. A top and bottom and aim just below the "equator" and in the vertical center.