Which atmosphere did you set for the trigger?
I followed your steps to the letter, with an atmosphere trigger set to ATM_Default, and I get this:
https://drive.google.com/file/d/1uyqJdSuADxk4rW3U9aJmRnBnkTHEnk5G/view?usp=sharingI'll try again typing the numbers in for the atmosphere box (position, extents etc) from your screenshot so im identical