If the earth was flat, with a telescope you would be able to see the whole mountain (mentioned in the experiment you referenced) and everything in between not just the top of the mountain.
Likewise from the west cost of the American continent you would be able to see the ice wall.
It seems to me that either of these would be easy enough experiments to perform if you wanted to prove that the earth was flat.
Why do ships disappear over the horizon if the earth is flat?
How could the people who walked across Antarctica do it in the time it took if Antarctica was a ring around the edge?
Why is there 24hr sun as ‘discovered’ by the flat earthers who went to Antarctica.
Every country on earth that has sent astronauts to the ISS must be working together to conspiring against us.