I think it would be some variation on this arrangement.  This makes the displacement move inward.  Not sure whether the math applied here sets white to zero, however.  I think this sets middle gray to no displacement, in which case... you'd probably want to double the values shown here.  :unsure:

Hopefully someone has a less waffling answer.  :lol:  Or even an alternate approach....

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Cage can be an opinionated jerk who posts without thinking.  He apologizes for this.  He's honestly not trying to be a turkeyhead.

Cage had some freebies, compatible with Poser 11 and below.  His Python scripts were saved at archive.org, along with the rest of the Morphography site, where they were hosted.