I've needed a few minutes to understand this:

Preview:

Environment preview: set to 90° instead of -90° (its default position)

Render:

In fact: each time the Enviroment preview is rotated, I have to turn the Background node's rotation as well.
Remember school? 90° <-> 1.57 radians

Once setup to 1.57, accordingly:

That being said, one question remains, for me: I thought that HDR's gamma value was to be set to 1 but in Poser13, this factor doesn't seem to change anything.

𝒫𝒽𝓎𝓁

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