The refraction from the Earth’s atmosphere lets you see stars 2 degrees below the horizon. I don’t know how that would translate for an object on the surface.
The curvature for ball-earthers, as you can see, is extremely steep. At one mile it’s six feet, which means you would not be able to see anyone with a big focus camera at one mile, they would be underneath the curve.
It’s also extremely Biblical as all the numbers for the curvature and spin on ball earth are weirdly either 666 or some derivative.