You should follow manufacturer's instructions and also follow your fire codes. I understand what you are saying about the visual space problem you'd encounter with a mantle two feet above the fire box. I believe there is a formula that you can use to determine according to fire codes how far away your mantle should be from the firebox it's based on projection of the mantle from the wall. For example, a mantle that projects 12" from the wall needs to be further from the firebox, probably 2 feet. A mantle with a projection of only 6" can be closer to the firebox. At one time I found this formula and determined that our 8" deep mantle could be 1' from the firebox and we were able to have more space above the mantle. Look up your local firecodes and see if you can find a similar formula for your area.

for a traditional fireplace, you would need to look up the code where you live. I believe the code is usually expressed in terms of x inches from top of the fireplace opening. So you would need to know how high the top of that is first. I have no idea what code is for electric fireplaces (assuming this is one that heats the air. If it's just a screen that shows a merrily burning fire but produces no heat, like our local sandwich shop has, you can probably do whatever you want.) Also, the TV may have it's own specs that say "must be X inches above heat source to avoid damage to TV" though usually you can reduce this distance by having a deeper mantle, or by having the TV recessed so the heat passes in front of it instead of washing across it. I suspect that for that it may not matter if the fireplace is gas, electric, or wood, as if it is hot enough to heat the house then it is hot enough to damage the TV if the TV gets to close. But I haven't looked at that explicitly.

Could you possibly post a picture of the area?

I don't think the shelves are finished either. Are they adjustable? Plants in shelves look a bit on the dorky side, especially when they match and aren't real. Consider 1/3 books (standing, leaning, lying, supporting other objects,) 1/3 large decor items and 1/3 open space. Do the shelves not continue to the right side wall? Looks like an odd gap there. I agree that painting the wall and that gap to match the shelving white will be helpful. Notice the unity of color here, but the finish on the woodwork is more of a satin or semi-gloss. I always advise putting TV elsewhere. General rule for me is that whatever hangs above the fireplace should be no wider than the firebox opening. A larger TV there won't help anything. Art would be my choice Note that in the pic here only the ceiling is reflected by the mirror. I'm sure if you sat in the right seat you would see the light fixture doubled, but still, art is just more interesting and exciting and makes its own focal statement without anything on the side walls. If you must have a larger TV there, then I would change the paint color to all black.