Disable part of a touchscreen from taking phantom touches
You can use the overscan subcommand instead of size for achieving your objective.
The syntax is adb shell wm overscan left,top,right,bottom, where left, top, right and bottom are the coordinates relative to the actual edges of the screen.
So, in your case, you should write adb shell wm overscan 0,100,0,0, to get a resolution of 1080×1820, as you have mentioned above.

Explanation: This will set your device's screen bounds to 0px from the left, 100 px from the top, 0 px from the right and 0 px from the bottom. See this image: