What's that, Miss Nancy? This is not a distance fall-off shader at all, nor is it a depth fall-off shader. In either case I would have used the P node.

It is an Edge_Blend fall-off shader, which is based on reality.

The variation in reflection comes from viewing angle here, not from distance or height or anything else.

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Renderosity forum reply notifications are wonky. If I read a follow-up in a thread, but I don't myself reply, then notifications no longer happen AT ALL on that thread. So if I seem to be ignoring a question, that's why. (Updated September 23, 2019)