Referring back to setting up a non-linear falloff for the Poser atmosphere's DepthCue, way back in Jul 2010 on page 3 of this thread with bagginsbill's post that endedwith,

b = x / (1 - .5 ^ (x / h))

Wow - Yay! This is exactly the compensation function we need to make the Poser Atmosphere attenuation function do what we want. We need to plug a node network into DepthCue_EndDist, also known as "b", that implements the function we just arrived at.

Great. So all we need is the distance from the camera to the point being rendered.

Uhoh. There is no node that does that. I wish there was. Are we dead?

Nope. If we accept a tiny bit of manual work setting up a shader, we can get this done.

But ... it's really late and I've got to go to bed. So, more tomorrow."

followed by the tantalizing question on page 4 that ended bagginsbill's penultimate post that same day:

...can you figure out how we can calculate the distance from the camera to the object?

I've searched the rest of the thread, and I've racked my brains - but I just can't find/figure out the answer.

Can anybody enlighten me?

??? In the Poser 9 material room how can I get the distance from the camera to the point being rendered ???

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The 3Dcheapskate* occasionally posts sensible stuff. Usually by accident.
And it usually uses Poser 11, with units set to inches. Except when it's using Poser 6 or PP2014, or when its units are set to PNU.

*also available in ShareCG, DAZ, and HiveWire3D flavours (the DeviantArt and CGBytes flavour have been discontinued).