yes, one would just need to replace the values in the following line by material or entity skills:
Code:

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Out.Fog = (In.position.y/1500)-0.25;

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the 1500 is used for scaling the fade. and the other number goves a density offset. just change the values and see what happens

btw, you can use the following line and set a vertical offset by the new value:
Code:

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Out.Fog = ((In.position.y-1100)/1500)-0.25;

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