Directional Inscattering Cutting off ?

I’ve exaggerated the Exponential Height Fog in this screenshot to show the effect I’m getting here…

I’m trying to get the fog to go white instead of blue at a distance. I’ve used Directional Inscattering to produce white fog, but as you can see, this suddenly cuts off for some reason. Red arrow is the direction the Sun is coming from.

Any idea why it’s cutting off, and if there’s a workaround to get all of the fog to be white?

Fog settings in a follow-up post, because I can only embed one image per post.