It's very simple actually. No need for extra long Allen wrenches.
Just remove the left lamp board and rotate the spider so the set screw is on the left side. It's only about 3 inches in - close enough for a standard Allen wrench.
The pictures show the wrench I used, and how far it needed to go in to reach the set screw.
And as others have stated, I can't over-emphasize enough - DO NOT OVERTIGHTEN that screw. It's way too easy to crack the plastic. Just snug it down.
ss_spider1.jpg ss_spider2.jpg ss_spider3.jpg