It should be extremely easy to calculate the moon's altitude if it really is as close to the earth as flat earthers say. All you need is two people in two different locations that are a known distance apart to simultaneously measure the angle that the moon is above the horizon.
In this diagram, an observer in New York and LA would each measure the angles, which would be theta 1 and theta 2. Using the law of sines, one could calculate the length of the other two sides of the triangle, and then use simple trigonometry to calculate the length of the dotted line, i.e. the actual altitude of the moon.