Why does my screen look slightly bowed or concave in the middle at the top when watching certain shows? I notice it when the screen is in letterbox more times that not. Is there an adjustment for this?

Is the base of the Tv sittling completely on a flat surface, no edges hanging off? There are some minor physical/mechanical geometry adjustments but you really need instructions to know how to proceed.

Yes, it's on the base that is made for the TV.