I just checked bb's EnvSphere notes again... this is what he says for Poser Pro...

If used in Poser Pro, the use of PPro built-in gamma correction may produce undesirable results. If you're going to use Poser gamma correction, set Gamma In and Gamma Out = 1.0 in the EnvPanoramic and EnvPanoramicEffects shaders. The effects will produce different results in PPro+Gamma because it changes the interpretation of shader colors.

"If I were a shadow, I know I wouldn't like to be half of what I should be."
Mr Otsuka, the old black tomcat in Kafka on the Shore (Haruki Murakami)