Is it more efficient to have the air condition evaporator coil place in the attic of the 2nd floor of a two story home or have the evap. Coil place in the attic above the first floor and then run the duct up to the 2nd floor and down the 1st floor? I was told that it is more efficient for the evap coils that service each floor should be above the ceiling for the floor they service. Is this true?