It starts 5 or 6 pages in.
This is what I was talking about before.
This forum makes it possible to link to a single post Robbyj. Tom does it all the time when it suits him. Link to your cited reference if you reference a thread. Don't make people hunt for it.
As to the math here, yeah, not going to touch that. Well maybe only in passing and partial coherence...
The air beneath the object creates drag, we got that. But without something pushing the object down, then it doesn't matter because drag would never come into play.
In FE, without the force of gravity, there are no balanced forces. The "falling" object will continue to accelerate due to the passing air (drag) until it reaches g relative to the Earth's acceleration. Net acceleration between the two becomes 0 and relative velocity becomes constant. That's terminal velocity, as quoted in the diagram.
I tried to run the mountain top argument for a while, and getting just the party line, gave up. The mountain top argument is that you weigh less on a mountain top, so how can upward acceleration be constant? The party line is that the celestial bodies pull upward with some kind of I don't know, gravitational force maybe? While minimal the apparent G force in RE decreases with elevation, but G forces have little to do with Terminal Velocity AFAIK, at least inside the denser gaseous parts of the atmosphere/atmolayer. With the almost unbelievable heights that extreme skydivers can reach nowadays you would expect a noticeable upward pull on downward acceleration and therefore sliding scale for terminal velocity based on starting elevation.
Lacking that FET should still be able to show that the starting fall acceleration of a body at the elevation of say Everest, or a body half that height even would be measurably slower than the starting fall acceleration of a body at sea level due to upward celestial pull.