The arch was the specification.
The fireplace sits on the kitchen wall between the range and refrigeration, directly opposite a large stone island. Its shallow brick arch is part of the room's architecture, so a stock rectangular screen would have left awkward gaps and hidden the shape that made the opening distinctive.
The approved drawing records an overall width of roughly 53 1/2 inches, a height near 32 7/16 inches, and the radius required to follow the masonry. Those dimensions became the fabrication reference rather than an assumed nominal opening.