The Real Question is Heat, Not Height
Electronics fail from sustained warmth long before anything looks dramatic. A fireplace that pushes its heat straight up the wall will cook a television slowly, and no mounting height fixes that.
Some units are engineered for this—a forward-facing louvre, a cool-wall design, or a top vent that throws heat into the room rather than up the face. Those are the ones to ask about by name.
Ask for the Mantel and Clearance Chart
Every manufacturer publishes minimum clearances above the opening, and they vary widely between models in the same catalogue. That chart, not a rule of thumb, is what your installer works from.
If a shop can't produce it for the unit you're looking at, that's worth noticing.
The Utah-Specific Wrinkle
Homes at elevation often run their fireplace harder and longer than the same model would work at sea level, simply because winter is longer and colder. A marginal clearance that survives a mild climate gets tested here.
A shop that installs in Park City or Heber every winter has seen the failures and will steer you accordingly.
If You Already Know You Want the TV There
Say so on the first visit, before anything is chosen. It narrows the model list immediately and saves you falling for a unit that can't do it.
It also changes the framing and the electrical rough-in, which is much cheaper to decide before the wall closes.