Ok, thats looking strange like a bug in P12. The P12 image is having worse resolution accordingly to 72 DPI.

But again the dialogs showing nothing about a real inch size for the images. I don't have P12. Is it possible that there is a inch scaling value for the rendered output. Though that must be tiny cause Poser is reducing the DPI but seems not to enlarge the inch by inch scale. Otherwise both images should look equal.

Here I'm finished with my experience. Looks like a job for the Poser developer :-( ... I'm waiting with my P12 money a further round ...