Hi everyone- I'm about to do a fireplace surround, but I am hung up on the proportions.

My (woodburning) fireplace is on an angled wall that is 70" wide and 96" tall. The firebox opening is 28.5 x 21", and it's 6" off the ground.

I want to recreate this surround, with the shiplap.

But I can't settle on the dimensions. I have one that is smaller, one that is a bit bigger, and one with the bigger surround, but a narrower mantel.

What does everyone think? I will need small finishing trim on either side of the shiplap, so that will probably be about 1.5" on either side.

Sorry for the 54,934 photos in this post. Thanks for your help!!!