Unless you have to have the wood a certain height from the flame, it's just personal preference. I like the look of the inspiration picture you attached better than symmetrical all the way around. But that is just my opinion. This is your house and you should do what will make you happiest.

We're trying to get ours as low as possible too but it comes down to code around here. We need around 19" above the top of the firebox with an 8" mantel (the required height increases the deeper the mantel is). Check with your inspector - your fireplace installer probably also knows the code for that.

@dbrad, we need to have a 12" minimum from the firebox to the bottom of the mantle. Our builder says it will look squatty going so short with our 10 ft ceilings. I am not convinced, but of course, I can't really tell until it is in the house... but, then it will be too late to change. Thanks for your input.
@BCB, thank you. I think the inspiration pic has a bit too much stone above the firebox, but it is very close to what I am hoping for.

I think what you're planning will be fine. To give you an idea, my fireplace is wider than it is tall but then again, my house is craftsman inspired and that was standard for the look. The sides are each about 15" wide to the mantle on the sides and about 11" high. I don't have a raised hearth though, so my fireplace box "sits" on the ground.

So, Virgil, my question is what is the correct proportion?

I'm going to wager a guess it has something to do with the Golden Ratio.

I'd keep the mantle as low as possible. The TV often gets put above the fireplace, and it's always a compromise. It is arguably the worst place to have it based on: 1) aesthetics, and 2) the neck strain it can induce having to look up at the TV. My TV is in the living room, but I purposely placed it on a low table so the bottom of the TV is about 20" off the ground. That way I can look straight ahead at it when sitting on the couch.

You can avoid the problem of the TV being too high over the mantle by using a Mantle Mount.

This is a great time to have elevation drawings.... you're squeezing a lot in there.

Yes, I feel like we’re squeezing too much in if we go with a 16” raised hearth. The problem is that the firebox is already set. Is it going to look odd to have a 10” raised hearth and then a few inches of the black firebox showing on both top and bottom?

cpartist-

The mantle mount seems like a good idea...as long as you're not wanting to use your fireplace at the same time. Sensitive electronics don't like extra heat.

It will look better covering the black of the fireplace like your inspiration photo. Jeffrey R. Grenz, General Contractor is right it's time for a good elevation drawing.

The inspiration fireplace on your wall, and the same fireplace with the mantel lowered:

groveraxle ... if you could photoshop some Caryatids to support the mantel I think we'd be all done here.

cpartist Your fireplace and the whole room looks charming and inviting. If I ever get called on to do a true craftsman, I want you on my team.

"...So, Virgil, my question is what is the correct proportion?..."

As my photo shows, in the majority of situations a vertical proportion is more timeless and pleasing than a square or horizontal proportion.

Groveraxle's photos demonstrate the better aesthetics of a vertical proportion, don't you think?

TVs are really irritating for those sitting around the fire and trying to read. Put it in the basement or out in the garage. Your life will be better for it.

cpartist Your fireplace and the whole room looks charming and inviting. If I ever get called on to do a true craftsman, I want you on my team.

Thank you!

I like grovers second drawing better. The first one looks top heavy to me.

Love Cps fireplace. i mimicked CPs proportions somewhat although mine is not craftsmen style. Very nice proportions imo. My fp sits on the floor and I have 7" of black metal on the bottom. It will be tiled just like the top and sides.

I like the taller one. Because you have a raised hearth, it changes the visual proportion significantly.

Cpartist's dimensions don't apply because her design is Craftsman with differing proportions and her hearth is flush to the floor.