Uniformity and settings
What you're seeing is a uniformity issue:
If you read my review linked at the top of the post, you'll see that the sample I reviewed did indeed suffer this issue.
There isn't much that can be done in settings to reduce it, and neither I nor any calibrator I know makes adjustments to try to reduce it. Feel free to try various settings, including adjusting local dimming, to try to reduce it, if you'd like.
Since local dimming can make black levels deeper, and deep blacks can make some kinds of uniformity errors more visible, then lightening black levels could conceivably make your uniformity errors less visible (of course, lighter blacks make the entire picture look washed-out, so pick your poison). Rather than monkey with local dimming, the easiest way to lighten black levels is to simply crank the brightness control. Other controls to try are backlight and contrast.