i created two Postprocess like the video you posted.
One at 3,000(xyz) and another at 2,000 (xyz) with ‘set AHR Bounds’ enabled.
My lost ray color was set to Black.
Playing with it has no effect, and changing the bounds dimensions doesn’t solve the problem.
I should add that i have successfully made several open scene maps to test and it works perfectly. just not the closed scene it seems.