Ok...fluid dynamics is a 'wierd science'. (no pun intended).
You have 3 basic filter types to consider. First is the replacement K&N flat panel. Then there are 2 types of cones, and these act slightly different.
The flat filter doesn't provide uniform flow. You have a square box feeding a round hole. Too many twists and turns, and not as much surface area as you can get out of a cone.
Replacement K&N: You are the air. Since you need the stock airbox to hold the filter, you're entering the stupid snorkel, as well as any extra holes you punched. Twists and turns. THEN you go through the filter. After the filter, some of the air has to travel farther than some of the other air, as the outlet from the box to the plenum isn't centered. The air actually has to make at least 4 turns even if you have the box gutted.
Standard Cone: The air comes in EVENLY around the entire circumference of the filter. It makes ONE turn, less than 90° (because of the taper of the cone), and heads up the pipe. More surface area than the flat panel (more important in a SC car than NA).
Cone with Velocity stack (can draw from the end as well as the circumference): This filter not only increases the surface area, but also causes a venturi effect. As the air entering from the end passes the main body of the inside of the filter, it DRAWS air into the filter from the circumference. From K&N:
Not only does the XStreamŽ add filter area, it actually redirects airflow inside the filter to pull in more air through the side pleats for even greater performance efficiency.
Does that make more sense?