DId you ever solve this? Ive notice the same in that situation with units that are just off the cieling. My read on it is that those sort of areas are only lit by quite a lot of bounce light and so it’s harder to get that smooth quality there.
One solution I found the helped a bit is to use rectangle light in the windows instead of just relying on the sky and sun but that does depend on the window sizes a bit. You could always fake it and add a couple of rectangle light on top of the units just to bounce light up to the cieling