I think the biggest factor when dealing with FPN is keeping your histogram full .
You may be onto something. I remember an issue with either the DVX or the HVX where, in a dark scene, if there was at least one small area of bright light, the shadows would remain black and punchy. But if you panned the camera so that the entire screen was dark, the blacks would get noisy and ugly. I may try an experiment with two scenarios:
1) A well-lit shot that has a face with skin tones one-stop "underexposed" but with nothing else in the scene brighter than that.
2) Same as above but with something in the frame much brighter (almost clipping) so that the histogram shows something near the right side.
Compare the two and see if it makes any difference.
Hmmmm.