Ducted A/C Unit - Bypass Ductwork for Better Cooling??

I'm not sure the exact model but a duo-therm.

I believe it does better primarily because it moves more air and is only cooling about 2/3 of the rig when the grate is open. The ducts are limited by the space inside the roof and restricts airflow.

With two units, I see far less benefit to ducting (assuming you have the power to run both).