I stock prefilter on the top of the intake is useless. It stopped hardly any dust on mine. Luckily I put a uni and a outerwear prefilter on it with .5 miles on it new. The outerwear prefilter caught the dust before it got to the uni. The uni was clean after about 120 miles on the first ride. Now I have a outerwear prefilter on top of the intake tube & over the uni. S&B is next.

If you look at the bolt that mounts the intake tube covered by that sock, the fit is so poor that there's actually an open part that allows dirty air to go right under the elastic and into the intake plenum. That ridiculous sock is obviously a hasty afterthought. I think that somebody screwed up and there was a major error in molding a proper manifold to connect the intake plenum with the between-seat grill, and CF Moto was too far along the scheduled rollout of the machines to afford the time to fix it properly, so they'd have screamed at their engineers, "Do something so we can sell these things!"
No self respecting engineer would design a motor vehicle intake system so that it draws air from the hot and dusty motor and back tire compartment.