The offset is ~290px to the left for me (the far right is just 290px of white). I have three screens with their tops aligned, from left to right: 1440x2560 (rotated so bottom of the monitor is now to the left); 3840x2160; 1440x2560 (rotated opposite to first monitor). Ubuntu 18.04.3 LTS. I configured the monitors using NVIDIA X Server Settings.
The offset is ~290px to the left for me (the far right is just 290px of white). I have three screens with their tops aligned, from left to right: 1440x2560 (rotated so bottom of the monitor is now to the left); 3840x2160; 1440x2560 (rotated opposite to first monitor). Ubuntu 18.04.3 LTS. I configured the monitors using NVIDIA X Server Settings.