Buckbuster' s diagram is correct according to everything I have read and tried. You should shoot the horizontal distance. I use a no-peep and it helps me maintain my form. The only thing I would add is that if angles are REALLY steep you should take into acount that shooting the horizontal distance would cause you to hit the proper spot on the hide. Since the vitals are inside the animal I believe that to hit them properly that you must aim a very small amount low when shooting uphill and a very small amount high when shooting downhill so that you are at the proper height in the center of the animal. For shooting at flat targets the horizontal distance has always worked for me.