So I have a very simple experiment in mind that will completely disprove flat earthers. Ff we can get someone living in a highrise or a high point that overlooks the ocean to get a tripod with a pipe fastened to it at eye point, then if the angle at sunset is below the zero degree mark, then it will prove that the earth is round.
Here is my logic. Flat Earthers believe that the sun never sets but moves around the flat earth. If they claim that it revolves around t he earth you simply ask them why it isnt dark on the entire planet at once.
Back to the tool, referring to the model, if the sun maintains the same distance from the ground, then the angle of view will never be below 0, but if it goes below 0 then the suns height must change in perspective to your location and goes lower than it.