Mach, something that you should consider;

In every lense that I've seen (stock, Darkstorm, and yours from the photos), the hole for the knob is a strange size. While it is much bigger than truly necessary for the knob shaft to pass through, it is too small to be optimal for LED backlighting. Although in practice the lens doesn't appear to tint the backlighting effect (with smoke anyway...), it must be reducing the light output.
I wonder if it's worth enlarging this hole so that it doesn't block as much. Note that this hole doesn't usually sit perfectly concentrically around the knob shaft, so you wouldn't want to overdo it.