I was told that an over/under package unit such as Trane (TCH) XR13h moves more air and has a higher static pressure than a mobile home package unit such as Trane (TCK) XR13m. The salesman said the TCK is designed for the air to rise since it is placed at bottom of mobile home and moves less air. I think he was blowin smoke. My original ductwork was over under but converted 15 years ago for a side by side package unit. These guys want to go back to over under. What is your pro opinion?