I seem to be struggling with the Sun/Sky system and physical camera approach. As you can see from the image the centre of the scene (where the sun target is pointing) is very bright and seems to decay accross the rest of the scene. I would expect to get a more even light for a sun and not something that resembles a spot light.
Try to turn off vignetting in phys.cam. So your scene brightnes won’t fade. As vignetting is kinda of (basically) radial gradient with the most bright spot in the middle and the least bright on corners…
What you get is due to the < vignetting > effect from the camera. Try turning that off. Also play with the other camera parametes, to get your light better.