Good  job.

The reason you may or may not need to do Displacement - .5 is that you need to take into account that displacements can be positive or negative. In a image map, this is handled by letting 50% gray represent "no displacement". But numerically 50% gray means .5 times displacement,  White, numerically 1, means 100% displacement. Black, numerically 0, means 0% displacement. By subtracting .5 (50%) you get the following:

100% => 50%
80% => 30%
50% => 0 % (No displacemnet)
20% => -30%
0% => -50%

The other issues of why this is not working out for you perfectly may have to do with the scaling. You need to get the total displacement amount to be the same as was internally used by ZBrush before converting that to an image. I don't know anything about Zbrush so can't help with that.

The other thing that may be different, is it looks like ZBrush was starting from the premise of un-smoothed polygons. So perhaps you should turn off smoothing on this figure in Poser. The small curved waves below the "ear" look like mismatch on smoothed versus unsmoothed low-poly.

Remember that the purpose of smoothing is to make a rough, choppy, low-poly figure into a smooth one that looks very high-poly. It is an automatic form of displacement. But you're trying to get the ZBrush defined displacement to do that. As a result, you may have BOTH going at once.

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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)