VRay Environment Fog weaker when duplicated

[Furnace]

Hi all,
I have a section of tunnel that I'm duplicating, the section lights look good on their own, the volumetric look is fine (attachment 01), but as soon as I duplicate the section the lighting loses it's definition (02), I'll add my settings.

Any help would be much appreciated.

Thanks,
Elliot

[Svetlozar Draganov]

Changing Environment Fog depth will change Fog appearance also.
In your case the Fog is not the only thing that changes - the whole scene is changed.
The Fog looks stronger in the section-scene because it has only two lights and the background is darker.
The complete scene has a lot of lights with very uniform distribution and because of that individual volume lights are not distinguishable.
If you want to get better definition of the light-volumes you have to use a lights with direct illumination.
Here is a sample with V-Ray Lights with Directional parameter set to 0.35:

Higher Directional values will produce stronger contrast:

Scene: http://ftp.chaosgroup.com/support/scenes/fog09.max

Can you post a reference image of the result you are looking after?

[Furnace]

Thanks for your help Svetlozar. My directional was only set to 0.2 so I've upped it to 0.5 and this has made them more defined.

Your help is much appreciated,
Elliot