S900-28 Yellow Tip Spiral Balance

I ordered two S900-28 from your company and upon installation, the spiral rod pulls completely out of the metal tube when the sash is closed. There is about 1/2" space between the bottom of the metal tube (not the yellow tip but the aluminum tube itself) and the spiral rod where it has pulled out of the tube. I measured my old spiral rod and it is 1/2" longer than one I ordered from you (when the spiral rod is pulled out of the aluminum tube and the lengths are compared).

Obviously, I need a longer spiral balance. Should I order a 29" or 30"? If these lengths are not available with a yellow tip, which color should I choose?

Thanks.