TV Mounted above fireplace mantel - neck strain?

Neck strain or eye strain (having to look ’up’ from straight ahead) will be a function of screen center height, viewing distance, and viewing angle(any upward angling of the eye).

I don’t have my big screen over the fire place, but I do have it wall mounted because of room constraints.

I did some calculations for my room and got the screen center set to give zero eye angle up with my comfy couch. No neck strain or eye strain.

Depends. If you are close and the screen center is high up - they yeah - it could be an issue.

I won't get into WAF or other decorating preferences.  Strictly from a 'human factors' standpoint - it can be done.

All of mine are at eye level except office.
There, top shelf = neck strain.

Not a fan or tilt and lean. Straight ahead. Wherever you put it, watch out for glare and reflections.

I dislike too high.

also consider proximity to speakers, l/r imaging height, and, where center speaker is to anchor the dialog to the screen.

I have found, directly below the monitor works best for center.

I have been able to blend this into several situations

https://www.ebay.com/i/233696110070?chn=ps&norover=1&mkevt=1&mkrid=711-117182-37290-0&am...

never considered getting anything different.

Stand up, relax, and notice where your eyes normally look. You’ll notice that our resting eye position has a field of view approximately horizontal with our forehead, downwards. Approximately.  If you say you are looking straight, it's not actually your resting point.  Your mind is just conscious of it and forcing it ahead.  Relax  your eye muscles and your view will shift down. 

That is, our eyes are naturally looking below horizontal. This is why ergonomic guides suggest the top of your PC monitor be at forehead level, and why people who raise up their monitors have an S shaped neck. They hunch over and raise their heads. Bad posture!!

So, if you plan on watching in a recliner, up is good. Otherwise, having the top of your TV about the level of the top of your head is best.