The earth curvature effect has been "explained" by the Flat Earthers' modification of their model to say "Okay, the Earth is a basically flat disk with a gentle curvature." But this by no means fixes their problem, because it is easy to use the visibility--versus--distance to calculate the radius of curvature of the Earth, and it is not a gentle curvature; the curvature does not have a huge radius, but obviously has the radius of our spherical Earth.
I am not a proponent of flat earth, but I will bite on this one.
I have used a spotting scope to watch ships on lake Michigan long after they went 'over the horizon'.
And I have stood on the shore of Flathead Lake and on a clear day, seen the beach at Polson, some 50/60 miles away, with my own eyes.
Neither one should be mathematically possible.
I have also stood upon the very summit of the continental divide, and could detect no curvature looking eastward. One should see a 'falling away' north and south, which is not apparent.