The one thing that does constrain the factory engineers is cost. What they engineer is the best compromise between quality, performance and cost. If you throw out the cost factor, many better options can sometimes be found. But it is tricky. Without their test facilities most times it is just a guess or depending on the aftermarket engineers and believing what they say. I never really went for what the K&N guys sold. My former job was as a engineer with Fram for oil filter and air filter media and manufacturing systems. Air filters are really pretty simple. Surface area, pore size and depth are the main factors involved. Oil adds a bit of "stick" but can also foul things up if overdone. Not to mention that cleaning one is rarely done well. Electrostatics are better way, but are for now best suited to stationary applications.