Tom, have you not seen the animation on the wiki? It shows the sun spinning around the north pole (for some reason) and only lighting a small portion of the Earth, looking like the effect you get shinning a flashlight towards the ground.
Maybe nobody used the word "flashlight", but that is a good description of what your animation shows. ("Your" referring to the content of the site, not you personally of course")
I have read many of the convoluted explanations of how sunsets works, they mostly seem to be explained from the observers point of view. Has any FE believer every really explained it from an outside view?
Maybe the way to ask the question is this: If the sun radiates light in all directions, some distance from the Earth, what happens to the light that left the sun heading towards the far side of the flat Earth? Shouldn't light heading outward in all directions reach every part of the disk at all times?
It can't be explained with a lack of intensity. If the sun was above your opposite point on the far side of the disk Earth, it would be at most about 4 times farther away from you. Light decreases with the inverse square of the distance. If it was 4 times further away from you, you would see 1/16th of the light. That is still quite bright. I experienced the total solar eclipse a few months ago. When the sun was eclipsed in the upper 90 percentiles it was still too bright to look at directly.