hmmm – in some of the clamshell kilns I have seen, keeping glass 3″ away from the elements would render the kiln useless. It would help to know how big your kiln is (especially the interior height), how tall your posts are, and how deep (tall) your molds are. I know I have had pieces within 2 inches of both side and top elements in my Jen-Ken kiln and not had problems.
I recommend that you talk to the dealer you bought the kiln from, or from a local glass shop/studio that has experience using the same kiln.
Fused Glass, Wood, Beads, PMC, Ceramics
Usable and Wearable Art
Art for the Sake of Art