I had the same problem with a DSA fork that used to be threaded but had the threads sanded off, so it had a smaller diameter than normal. I highly doubt it's the SCS itself. Make soda can shims. Cut soda cans into pieces that are about the size of the part of the SCS that clamps onto the fork. 2 usually works. Stretch yo SCS, figure out how to get the shims in there (it takes some work) and you'll be good to go. If your compression ring (the one that looks like a crown race with a slit in it) slides in super easy and your fork still slides out with no resistance when it's on, it's more than likely the fork, not the SCS. If not, then it's the SCS.