It is a very clever computer model, but it doesn't actually represent FET.
The firmament itself is responsible for reflection of light (like a reflecting window) which is why we get sun dogs and how the south pole can have 24 hours of light.
Most annoyingly, he has allowed you to change the height of the dome, but not the altitudes of the sun and moon independantly. He's got them up really high. Rowbotham had the sun at just 800 miles. I can't get them down that low. And they shouldn't touch the firmament. They aren't stuck to it.
But its his model and its very impressive from a programming standpoint.