With a telephoto lens, is it possible to zoom in on objects that are 20 miles away? Can you still see the base of that object if your elevation is equal to the base of that distant object? (assuming the air is clear that day of course)
If that is possible, then NASA and Merriam-Webster's measurements of the earth are wrong. They say the earth's curve is 8 inches of drop per mile squared...
20 miles away x 8 inches of drop = 160 inches (~13 feet below your horizon)
Image source: i.imgur.com/ewLBM1u.png
Oops, my bad, their chart says that if the object is 20 miles away, there's actually 3200.83 inches of drop.
So, that's 266 feet below your plane of view.