I'm just going to answer the point at hand, so that the globalists cannot accuse us of diverting attention.
This experiment is a classic objection to the flat earth. Thousands of years old,so I am not the first to successfully refute it, and won't be the last.
This experiment does not prove the flat earth at all. Why? Because the sun does not decline in the sky, it is only our perspective that makes it seem that way. As any object goes further away it has the appearance of getting "smaller."
This is what accounts for the angle differences noted in this experiment. It has nothing to do with the rotundy of the earth.
Here is a video explaining perspective.
There is no curvature on the flat earth.