I appear to be having some issues with setting up both Mist and Sun Beams for cycles in Blender 2.8. I'm attempting to to get a god ray/fake-volumetric effect from the window in my scenes. However, it doesn't appear that the rays or mist are being calculated correctly. It's supposed to look like a beam of light coming through the windows, now it just looks like a muddy mess!
Here is an example of what I want it to look like:
Here is the blend file as well if this helps any:
I'm using an HDRI map to light the scene.
This is the node set-up I'm trying to go for: