The problem is in my scene the actual horizon line (at infinity) doesn’t meet the end of my ground plane. When I enable the Sun Disc in the Sky Texture background (Nishita sky) the horizon line is clearly above as the sun is cresting the horizon. I also want to blur the sun image.
I figured I could render the scene with a transparent film background and then render the Nishita sky background without any objects in the scene after having rotated the camera such that the horizon line would have dropped. Then I can blur the background and composite it beneath my scene (after having blurred it). Is this what a new scene is for?