This thread raises an interesting issue that is testable. If the Earth is flat, then objects at a distance should appear smaller, but we should still see the entire object. If the Earth was curved, then we would see only the tops of the objects, since the bottoms would lay below the horizon. This is related to the pictures shown in this thread and the ideas discussed.
Hence, as a ship approached us, we would see the tops first in RET. This example is probably well known to the fora.
Now, one challenge to REers in regards to these statements is how do we demonstrate that the bottoms of the ships are not simply merging into the horizon line? Indeed, it is difficult to identify objects at such large distances with adequate resolution.
If we use a magnifier, however, we can test this scenario. Simply bring a pair of binoculars (or a cheap telescope) to the coast and use it to watch advancing ships. This is easy for me since I live in Auckland, which is a large port city with many ships arriving and leaving.
When you use an optical aid, you see definitely that the bottoms are below the horizon. Such observations are in disagreement with the FET, which postulates that you would see the entire ship.