I will quote it here: "Please assume in these examples that the mountain is sitting on an empty plain."
Where in the known world would this phenomena exist?
Lots of places have a mountain with a pretty flat plain area around it like this:
https://www.istockphoto.com/photo/big-empty-land-with-beautiful-mountain-background-in-mongolia-gm955711228-260936156
https://depositphotos.com/199534116/stock-photo-empty-land-sunrise-top-mountain.html
https://www.istockphoto.com/photo/empty-landscape-desert-mountains-and-flat-land-of-death-valley-national-park-gm1004021894-271209736
There are many places on earth with a large hill or mountain with flat plains around them. I grew up in Oregon, and Central Oregon has many, many places like that.
All of these photos you have introduced have mountainS visible in them.
Not simply a mountain.
You are mistaken about this.
Pete, I've come to realize that you have to always be right. Plain and plane have two very different meanings. A plain is a flat area of land. A plane is a vehicle that flies up in the air. You told him he was wrong about calling it a plain. Why would he be looking at a mountain with an aeroplane sitting next to it to view shadows? You appear to be a very condescending person. I've watched person after person ask you a question, and I've never seen you answer it. You just argue with the person, or accuse them of being rude. Why didn't you answer his question about the shadows? Or answer my question, which is why does the sun not just get smaller, but appear to be at the same level, which is what happens if you watch someone with a flashlight walking away from you. A spotlight, miles up in the air, would not appear to drop down and disappear bottom up, it would just shrink in size. I would also like my question answered about why your model of the sun doesn't show the "ice wall" receiving sunlight 24 hours a day for 4 months out of the year. Instead of picking on my grammar or the way I ask the question, you just show me the science behind your theory, and show me a working model that gives sun 24 hours a day in the extreme northern and southern hemispheres. Just answer the question please.
The word is "plane."
I suggest you research the word, "plane," as it it relates to FET.
FET will use the word, "plain," or its plural form in the same way as RET , but the OP was utilizing the word relative to the entire flat earth plane.
In which case, I corrected him.
Okay?
No; you corrected something I hadn't said. The word is NOT "plane". I was NOT utilizing the word relative to the entire flat earth plane.
I was utilizing the word "plain" with reference to a plain, i.e. a large, flat area with no hills in sight. Like what you would see in rural Saskatchewan. Or eastern Russian. Or beyond the Great Divide...there are lots of places like this. The guy who posted a picture understood.
And there doesn't have to be JUST ONE mountain, either. Let's not be silly here?
You are standing on a grassy PLAIN. With a mountain in front of you (or a mountain range, I don't care). In the other direction (behind you) there is nothing to be seen in view, except an apparently endless PLAIN. Since you can't see anything protruding from the surface in that direction, it stands to reason that nothing in that direction can be creating the shadow that is seen.
As the sun sets, the shadows goes up the mountain face. Simple geometry says that the shadow can't go up the mountain face unless the sun is sinking behind something. The "cloud lit from underside" theory doesn't accomplish anything here. We aren't talking about light sneaking in somewhere unexpected; we are talking about a shadow, the absence of light.
What's creating the shadow? What is blocking the sun's light that so regularly crawls up the mountainside, finally leaving it in shadow? If it is already dusk, why can I fly up in a plane and see the sun again? I haven't found an explanation in Flat Earth theory that explains this. Not saying there isn't one: if there is, I'd like to hear it.