Dont know if "gapping" is the word im looking for but read on. Consider the following; a filter rack with 2 oh say 18X18X1 filters. The return size is pinched down for what ever reason through the wall where the filter rack is. With the filters in place it makes a whisiling noise (yes all that said is a whole issue in itself but one question at a time) bothers the gal in the adjacent office so the staff routinley pulls the filters up to relieve the noise leaving about a 5-6" "gap" between the bottom of the rack and the bottom of the filter. My question is in theroy would (aside from the obvious reduction in return size) this also reduce the airflow since the air would enter in through the 5-6 inch gap of un-filtered space by virtue of the fact that its taking the path of least resistance as opposed to having the filters totally in place? Does that make sense what im trying to say here? Thoughts?