The extended filters like Hubbard has in his photo is cool, but IMHO, if offers nothing other than looking cool. No appreciable performance increase on a street bike. Not sure where the thought came from that a massive air filter was needed on a twin cylinder HD but the older air filter housing's that had the "coin slot" for air to enter did restrict flow, but the new filters assemblies on our CVO's flow more air than we can use.
Also do some research online, some educated folks feel the K&N style oil impregenated filters are not all they used to be on carb engines with Fuel Injection, that I don't have an opinion on, but I did stop using them 8 - 10 years ago on my personal cars and a few years later on the bike.
It does look cool to me, but it also serves a purpose. I don't claim to be a Mechanic, but I do have enough intelligence, and experience, that I've gathered over the years, to understand that our Motors are basically no more than an Air-Pump. I'm not an educated man, so I will try to share my limited knowledge on this subject in "Creek-Boy", kitchen-table language. How to get the most air into our Engines, and the quickest way to get that air out, is the objective. It's not the width, or surface area, of the filter, it's how close the backing-plate is to the throat of the induction module. So, the solution was gettting the back of the backing plate, which btw, had to be modified to accommodate the 64MM TB, off the front of the induction module. Put your hand directly in front of your mouth, and try to take a deep breath. Then, move your hand back, and take a deep breath. That's a lot better, ain't it? Got your lungs full that time, didn't you? So...the objective is to get the right air-induction system to get the air in, and the best exhaust, to get the air out. I know there's a little more to it than that, in Heads, and Valves, and Cams, and Pistons, and TB's, but that's what I pay Jody for. It's all about AIR. There endeth the lesson. Later--HUBBARD