I panicked last night.  Sorry.  I think the equation I want, which will integrate the negative 'difference' dial setting into the calculation of the main delta, would be:

final_delta = (source_vert + original_delta) - target_vert.

The equation seems to require that the difference between the two meshes be taken into account when adding the deltas.  Previously, I haven't considered re-calculating the original delta before trying to modify it by the difference between the two meshes.  But I haven't tested this yet....

Thanks for the response, nruddock.  Sorry I wasn't quite coherent in the message to which you respond.

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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.