You might find that the SCS is not actualy pushing the nub through the hop window.
I've found this with even the stock arm and barrel.
I widend my barrel window a little so as the rubbers nub can be pushed through the window unimpeaded, this also takes some of the pressure off the hop arm aswell.
I dont use the SCS as I dont like them, I do use to Madbull X/fishbone nub in 1 of my VSRs, I ground the original hop fangs evenly so the nub would sit inbetween them, thus giving me a reference point as to where the nub should be and holding it straight at the same time.