The AC professional says I have a bottleneck in the return for the downstairs AC unit. The unit is a 4 ton. Because of the way the house is constructed there is not a direct opening from the return air filter to the air handler. It makes a turn and goes between the floor joists for a short period. I measured the opening at 24" x 11". He recommends adding two 12" x 24" returns. Does this sound right??