If your light has a circumference of 75mm - the diameter would be approx 24 mm. That would indicate the sock for the Raider III/IV - they do stretch a little so if the end is a little bigger, it will slip through.
You could get the larger one and keep it in place with a double end bolt snap the hooks to the bungie on the sock and a ring on the back of your light. It may not be as stable, but it will work. Add a couple of wraps of tape and it would probably be a perfect fit.
I'd recommend the double end bolt snap for either, since even in the proper sock, the light moves and the double ender eliminates the possibility of losing it. If you look at the pictures on the bottom of the page for the light socks you will see the bolt snap setup.