by Erik Green
3 flows editing screen "size" - using superuser command 'wm overscan' - to choose from. One removes 30% from the top (Low) and two ALSO removing 15% for on either side (Left or Right).
Goes live directly when chosen flow gets selected and resets on 'Screen Off' or waving in front of the Proximity Sensor (0-4 cm).
Make a shortcut to one of your liking. I know I can make this way more complicated using user input values and multiple choice dialog. But I don't and won't. Just uploading something that helped me going CM from MIUI (which got a great built-in '"One handed mode")
Rate and review within the app in the Community section.