You are being silly, of course you can see everything coming from heaven since earth is flat.
Yea thats a good point. Not only a flat earth, but when Muhammad was alive, the size of the earth was probably small to him. He probably thought earth was really small, like the size of Arabia and Israel up to Egypt and Iraq. But there is no way that all of earth today could see Jesus descend from heaven. I have to ask a Sheikh this question one day lol. Of course, the answer would probably sound something like Allah knows best, or only Allah knows.