I found out what happened. The Noteperformer expression map has an override for playback timing humanization which is set to 0%, so no amount of change in the global plaback preferences dialog could have any effect. I copied the Noteperformer expression map and changed that setting so I can now apply timing humanization if need be.
NotePerformer turns Dorico humanization off, because it has its own humanization algorithms.
So, then…NotePerformer dehumanizes in order to humanize… 
Nice! 
I’m sure Arne Wallander will be pleased. 
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I see what you did there.
But “too many cooks spoil the broth.”
One has to turn off Dorico Humanization to create a known base for NP’s heralded adjustments.
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