You can tilt the panel and the picture will be good.
The issue is that it is uncomfortable to hold you head at that angle, llooking up from seated positions. By the end of the game or movie, you neck will be sore and aching.
The actual best position for comfortable viewing is with the vertical center of the panel below your line of sight at normal sitting position, however there are issues with obstructed view in a room, so the compromise is vertical center of panel at line of sight at sitting position. Of course people are different heights so perfection is never achieved, but perfection is not necessary, only general good practice.
Some people live with these over their fireplaces, but it isnt the best situation. There are also issues with actually using your fireplace, with smoke, soot, and heat negatively affecting the set. Not recommended.