You don’t. You avoid decorating the ceiling with fake stuff that make things look worse.

imagine the skeleton of the house.

Beams, faux or not should be where actual structural framing beams would be.

The are supposed to look like they are holding up the roof.

The reason many of these beams don't look good is that they're undersized and spaced too far apart.

Whatever spacing you choose make sure that the beams that land to either side of the fireplace are equidistant from the fireplace edge. You might have to adjust the spacing to make sure you end the room without it looking awkward.

It's a mystery meat with no picture, that much is certain

IMO fake beams always look like glued on after thoughts so at best they need to be placesd in the same way they would they are in the actul ceiling if you removed the drywall.

Too often we see ”beams” dead ending at the top of a window or the middlevof a fireplace.