Monitor manufacturers are quite smart, if you don’t mind us saying so. Long, extensive research established that because of the closer fit with the natural way humans see the world, it’s easier to calculate optimal viewing distances for curved monitors.
The number is all you need to know about the farthest you should sit from the monitor. Brilliant! Got a 3800R ultrawide? Plonk yourself no more than 3800mm, or 3.8 meters away. Chose an aggressively-curved, panoramic 35” display? Then 1800mm or 1.8m is your maximum seating distance.
Sit any further and the curve won’t cover your field of view, defeating the purpose of getting a curved monitor. Also, you’ll probably be too far to benefit from the monitor’s resolution and pixel density.