I've read this question, it's not helping.
I have two monitors, a 1920x1200 (DP-1), and a 1920x1080 (eDP-1) below and a bit to the side of the previous one.
xrandr's man page and some online reading made me believe that I could offset the bottom monitor with the option --pos.
This however:
xrandr --output DP-1 --above eDP-1 --auto --primary --pos 0x0 --output eDP-1 --pos 940x1200
does not seem to add the x-offset to eDP-1.
Adding the --verbose flag confirms this, I get:
crtc 0: 1920x1200 59.95 +0+0 "DP-1"
crtc 1: 1920x1080 59.93 +0+1200 "eDP-1"
x-offset is 0.