There's a delicately game of proportions here.

Frankly, a linear fireplace does not necessarily help, because a linear fireplace looks dumb all the way on the floor, so it will likely rise off the floor enough to offset the perceived height adavantage. Here are a few linear fireplaces, all of them finished in a very clean, minimal style, a few with TVs: http://pinterest.com/pyrotom/places-of-fire-linear/

One thing that will help tighten up the space is to use a non-combustible mantel (below) in place of a typical non-combustible surround (marble, tile, granite) and wood mantel combination:
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Thanks everyone! I have decide to just eliminate the fireplace.

Often the best solution to a problem is to eliminate the problem!

It's best to have the fireplace opening as close to the floor as possible so that the TV won't be too high for viewing while you are sitting down on the sofa.

Oh, I wouldn't eliminate it, I loved my fireplace with the tv over the top - I did not have a mantel it seemed too much with it. I had a beautiful 1/4" cubed stone tile (3 dimensional) going up the wall from floor to ceiling it was beautiful.