> Quote - Can you make it thicker at the top or bottom?

I'm fairly sure this can be done (to an extent) by using the Y component of a P-node to control the DepthCue distance settings. Unfortunately I don't have time to set up a test scene tonight.

By the way, for information.... when using DepthCue with reflections (e.g. water) there is a problem: the z-depth used to calculate the fog density is measured to the reflecting surface, not to the reflected objects. In the above image, for example, the reflection of the tree has less fog the closer the reflecting surface gets to the camera. This is clearly wrong, and I have not (yet) found a way around this, other than using volume.

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)