It has been said that you don't need an air filter on a boat that never comes to shore, and a plane that never lands. As long as the surface area is large enough and the mesh is large enough to be unrestricted, it should be fine. That would be less restricted than the carb by a large margin to allow for dirt clogging it. Nylons are probably OK, but over maybe at least a square inch. Not just the 3/8" or so that is commonly on an average motor. For myself, I am more concerned about clean fuel than the air. Cars are right in the dust and dirt though. Some guys that smash planes a lot like in combat place a piece of rubber tubing over the intake, so when it crashes, it seals it off. It still gets dirt in the bearings though. For flow simulation, you can blow through the carb hole, and then the filter and compare the restriction. If you want to spend time making a flow meter, and like that sort of thing, that is ok, but you can tell that way. As for funnel shapes, I doubt that makes any difference on 2 strokes. Maybe a 4 stroke with a high pressure blower of whatever sort. Welcome to the forum.