I probed about this in the questions and answers forum and have been mostly met with silence. As I haven't seen it discussed in the debate board after about a year of lurking I've decided phrase it as an argument for RE.
1) The sun goes directly overhead if you live on the equator, and if you live at a pole it hugs the horizon.
2) The sun is roughly circular in shape wherever you view it from earth, minor diffractions and distortions aside, it is never obviously elliptical.
2) The sun cannot be seen all the time by everyone on the earth. So if the earth is flat, the sun either emits light spherically and dips below the edge, or acts as a spotlight circling around the equator and does not dip below the edge.
3) If the sun dips below the edge it would pass directly overhead at the sound pole, which is incompatible with 1). Also the sun could not pass overhead all points of the equator in one day, it would be seen to hug the horizon at one place and pass overhead in another. So again incompatible with 1)
4) If the sun acted as a spotlight, it's shape would vary depending on your position on earth. At the equator it would appear more circular and at the poles it would appear as a thin ellipse. On the parts of the earth where the sun barely comes above the horizon it would practically appear as a thin line of light. This is incompatible with 2).
So as far as I can tell, RE models the shape and trajectory of the sun across the sky quite nicely and it doesn't tie in with FE.