is surface area. The greater the surface area the lower the flow and greater the efficiency through any given sq inch of the media. Obviously a wide open filter causes less restriction then a small pore size filter media, but the wide open media is like a chain link fence it sucks at capturing particles and it has trouble holding what it caught. The fibers of the media play a key part in the flow equation and the actual efficiency which is measured in ability to trap given size particles and hold said particles. The various bodies that govern engineering bodies such as SAE, Nat Fluid Power Assoc, ASHRAE and etc etc all dictate testing proceedures for the filters they use, using given flow rates and given size "test" particles, feed rates, flow rates etc.. I like to say that filter fiber sizes in scale are like this: cotton/cellulose = pencils and are considered primative, Synthetic's such as Pollyester/Polypropylene = toothpicks and glass fibers are more like needles in size, if you look at them all under a microscope. The fibers themselves are blocking/restricting flow. The smaller the fiber the less restriction, not amazingly high dollar and high performance industrial filters use the smaller tiny fibers, this allows greater flow, higher contamination capacity, less restriction and more precise particle control. When you buy a filter you are paying for the holes not big fibers to block the flow. Oh by the way, the use of oiled cotton gauze with "stcky" surfaces dates back to the time of using spanish moss as a filter media. it's primative. The modern small fiber filters physically capture the contaminants in the fiber matrix vs sticking to a surface.
So here is your answer, wrapping a filter media around a pleated filter is ass-backwards if filter efficiency/performance is on the line. Being denighed the pleating the wrap starts right off with less surface area.. Normally a prefilter is a really course media intended to get the big stuff out of the finer filter. No great wonder the high performance medias can be more tightly pleated then the bulky primative fibers. Finer media allows for far more surface area then the primative fibers. That's why a paper filter can easly have double or triple the pleats and surface area of a washable cotton gauze filter..
So the trick is first don't use an air filter that has holes so large you can see them when it's held held up to a light. Think about increasing the surface area by using a larger filter and or stacking two filters. Look at the NASCAR filter housing assemblies on eBay. The basses drop down and engulf the carb allowing a taller filter, the basses and lids are curved to encourage smooth flow and they even have walls to aim and stabilize the flow. For a supercharged motor like your building I'd suggest looking at a new GT500 air filter at the FORD Dealer it is the typical cone looking but is made of high performance media.
