One thing to note is that if your greyscale image has a more-or-less mid-grey base, with darker and lighter parts, it will not work correctly in Poser if you plug it directly into the Displacement channel.

Poser requires a value of zero (black) to give zero displacement, negative values (blacker than black!) to give negative displacement, and positive values (greys) to give positive displacement. 

So for Poser, you should stick in a math node to subtract (around) 0.5 from a mid-grey displacement map before plugging it into the Displacement channel. You may need to change that value for your map, or adjust your map to suit.

This may not be the whole answer, but it is possibly a part of it.

"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)