The FE map relates to the RE globe mathematically as a projection. If you take the surface of a sphere and project it onto a 2d disk, the only distances that are preserved, i.e. both the same, are distances along the north/south radians. Doing this gives a distance from north pole to equator of 6,215 mi. This matches gps, celestial navigation, time/speed/distance, google maps distance tool, etc etc etc. I have never seen a FE map with a scale, but this is one way to do it. If you use that scale on the FE map, the east/west distances are too long (vs all conventional sources) in the northern hemisphere and too short in the southern, which matches the distortion expected when projecting a sphere onto a disk. This is why on the FE map, the US is narrower than Australia, while in actuality, Australia is about 300 mi less east to west distance.

If you postulate that the edge of FE is the same distance from equator as from north pole to equator, this gives FE radius as 4 times 6215, or 24,860 mi (approximately). As I said, this matches RE geometry and observation, at least along direct north/south radians. But ... problems.

The FE radius is unknown. First, because FE maps don't have scales, so we don't know if they intend to match RE distance directly north/south. Indeed, one prominent FE poster said that no one knows the distances across oceans because you can't crawl across them with a ruler and that is the only way to measure. Second, because FE does not know where the southern edge of FE is. Some say it is an infinite plane, some say there are lands beyond , and no one knows how the dome meets the surface or where exactly it is down there. Until it is ascertained where the edge is and what the scale is, how can we know the radius?

If you take the FE north/south distances as the same as the RE distances, and you take the edge as the circle formed by the top down mathematical projection of sphere onto disk, then the diameter of FE is equal to the circumference of RE. But that requires knowing that the scale of the north/south lines on the projection is the same as RE and that the edge is where the circle would be with a mathematical projection of RE onto FE. Can we say that FE agrees these distances are the same, there is an edge, and it is the same distance from the equator as the north pole?

Seems to me that either the FE north/south distances are the same as RE, in which case Australia is too wide by hundreds of mile, or if the north/south scale is not the same. perhaps unknown, and the edge is not the same distance from equator as from north pole to equator, then how can we ever calculate the radius of FE?

If you take the FE north/south scale as equivalent to RE, then the FE east/west distances do match observations and RE does match. If you don't know the scale of the map, you don't know the distance across ocean, and you don't know where the edge is, how can you ever know the diameter of FE? I submit that either FE does not match observations, or we are all so ignorant that we may never know.

Or you could do the math for Eratosthenes experiment while assuming FE and get numbers that don't match anything, I guess. Then you have to explain everything from gps to airline schedules etc etc etc not matching. That will take a huge conspiracy involving geographers, cartographers, astronomers, navigators, geodetic surveyors, etc etc etc, all of which must either be sinister of unable to do math. I have heard FEs take the position that scientists are stupid and/or evil and actually no one knows because FE is a young science (not true) and does not have the resources to figure it out (true).

The last possibility is that our powers of observation are all distorted in the exact way to make FE look like RE, perhaps by some uber Einstein n-dimensional math. That leaves you with RE for all practical purposes and FE as a mathematical concept of ultimate truth. Not very useful or satisfying, except to be prideful or perhaps to make your preexisting beliefs (religion) plausible.

To know the diameter of FE, you have to have a map with a scale and know where the edge is. So far, I have only heard speculation on this from FE, but if you can define it, you can calculate. Then you can explain why it does not match observations, but that may be a different thread.

I welcome anyone pointing out errors of math or logic, and especially welcome anyone with a coherent logical explanation of FE diameter that matches observations.