This is how I pre-sight-in on mine. I shoot the first pin at 5 yrds. I get it center and about 1" - 1.5" high. Shoot 10 - 15 yrds to see where it hits. For mine, I put pin #1 at 25 yrds (in your case, 20 yrds). Now I repeat the above step at 25 yrds for pin #2. I then shoot 35 yrds to sight pin #2 in. I have 4 pins, but only sight in two pins. I don't shoot past 40 yards for hunting. My reason for pre-shooting high is so that I don't miss the target.