Although I am not familiar with the smackdown I do have the Limb driver that works really well for me.. Same principal for both.
Found this on you tube
http://www.youtube.com/watch?v=NXIt0igXLG4

If you follow these directions should be no problem. Looks really simple. Try turning cock feather up. Is your nocking point\d-loop too low? if so this causes tail low departure and probably causes contact with the arm of the smackdown even at it's lowest..
Try paper tune or walk back yet?