How big is your throttle body? Certainly not bigger than the available surface area of the filter. The most restrictive parts of the stock air box is the 180 degree turns the air has to make. If you opened up the bottom of the stock air box this would be a huge source of fresh air. The problem with conventional CAI's is that the bends cause turbulence, and the small space of the fender well is not ideal, because the surface area of the filter does not have much room to breath (think about breathing outside, and breathing outside with a helmut on)
An intake that has one straight shot to the throttle body, draws in cool air, and has an abundant source (the surface area of the filter is taken advantage of) would be the ideal intake, and thats exactly what this set up is.
The filter has very little to do with restriction, but I am using a K&N replacement.