For a start there is no 180 bend to get in the front (see pic), and second by coming in the side you are only exposing a 4" dia. area of filter to the incoming air and dust and the filter will block solid in that area quick smart. The round air filter is designed to recieve air on the front of the filter, thereby exposing the Whole of the filter to air and dust. I reached that "conclusion" by using commonsense, Regards Frank.

