What can I do if my projection screen shrinks when Duplicate Mode is applied in Windows?

The displayed image ratio shrinks because the projector adjusts the displayed image ratio based on a received resolution which does not match the output resolutions the projector is designed for.

Please follow the steps below if you would like to have the displayed image remain intact: 

Step1

Go to Windows Settings and select Display

Step 2

Select Advanced Display Settings

Step 3

Select Display 2: BenQ PJ, then click Display Adapter Properties for Display 2

Step 4

Select List All Modes, then choose an output resolution that your projector is designed for (as listed)