Or we could start with the part that is relevant to this discussion - the height of the sun and exactly how it can't produce the shadows shown in the video.
The Sun's rays are reflecting off of the Earth.
The kind of shadow being created by Mount Rainier is an "umbra" shadow. It can only happen with a point source of the light (i.e. the sun) and could not form from reflected light.
Your source?
http://letmegooglethat.com/?q=Umbra+shadowLight reflected off any partially reflective surface (One that is not a perfect mirror), especially a diffuse one like clouds, is scattered and dimmed and usually takes on the colour of the object reflecting it, if it has any. The shadows cast by a diffusely reflected light source are nebulous and indistinct compared to the sharp edges of an "umbra" shadow coming from a direct light source.
https://en.m.wikipedia.org/wiki/Diffuse_reflectionhttp://www.physicsclassroom.com/class/refln/Lesson-1/Specular-vs-Diffuse-Reflectionhttps://www.cheapjoes.com/artist-resources/artist-tips-and-lessons/artist-tip-1(Treated from an artistry perspective, but essentially verifiable by any amount of experimentation, as seen below.)
You can perform an experiment to verify this yourself by taking a flashlight and shining it on a wall.
Any object you hold up where the reflected rays of the flashlight can shine on it will be lit far less and will have a much less defined shadow line both on the object itself, and in the shadow it casts on a far wall than if it were being shone on directly. In fact, there is no way you can angle the flashlight to produce the same shadow either on the object or behind it that would occur if the object were directly in line with the beam.
Now let's consider what has to happen for this reflection to occur.
In our little mockup here, the flashlight is the sun, the wall is the cloud and the object is the mountain.
For light to be reflecting off the clouds from the sun to hit the mountain, both the sun and the mountain would have to be on the same "side" as the clouds.
According to the sacred text of the Flat Earth Society, Earth: Not a Globe by S. Rowbotham, (pg 99 and fig 66 on pg 129) the sun is always above the surface of the earth and the upper layers of the atmosphere, well above where the clouds are.
There is no configuration of the Flat Earth, it's sun and it atmosphere that can account for the angle, intensity and colour of the light shown in the video, or any other video of shadows cast at sunrise unless said sun at some point is at an angle that throws light upwards at the clouds. To do that, it must be below a projected line thay the clouds are above. No amount of messing with perspective and using arbitrary distances can get around this - if there is a case where this is possible, then precise measurements of distance and relative angle to the observer need to be proposed.
There is only one way around this: contravene this argument with numbers.
Tell us the exact height of the sun, the size of its orbital circle and the angle it makes between its position, its orbital centre and the height of the cloud cover and then we might have something to go on.
Otherwise, reflection is not a plausible explanation. At all.