About double the height of the vases would be nice. Yes. in a perfect world,.it could be larger .

I do not care for the mirror or the tall vases. (especially with the stems). The mirror is a little too narrow. Get one that is at least the same size as FP box and I would look at round instead. Bring in some color (from your room). If you stay with the mirror, get accent pieces that are oval or round shaped.

I'd go with a portrait oriented picture about 75 to 80% the width of the mantle:

Eclectic Living Room · More Info

Too small.

Too small. Terry, it's a reflection of their taste.

It does not appear that the mirror and be placed on it's side. Not even on both ends.

Pier 1 http://www.pier1.com/Gold-Waves-Mirror/2766580,default,pd.html?cgid=mirrors#nav=top&cgid=mirrors&start=1

Mirror reflects the white ceiling so kind of boring. Art would add color and interest.

Maybe not that much color!

The mirror should be larger and turning it sideways won't improve the situation. It will still be too short for the fireplace.