I'm not sure what the 2" and 1.5" refer to, but, on the honeycomb snap-ins, I calculate about a 60% reduction in air inflow area. That is, the 7 stock grill vents are about 180 Sq.in. total area, and with the honeycombs in, the total airflow area is just about 70 Sq.in. (the honeycomb holes are...