This is why the explanation about sunset doesn't work. Even if we accept that at sea level waves could get in between you and the sun thus causing it to block the sunlight, at any reasonable altitude you would be looking over the waves and easily be able to see a sun several thousand miles above the surface of a flat earth.
Right; at least if light follows straight lines. The smaller the obstacle, the closer to the observer it has to be. If it's a dime, it can't be down the pipe. Its impact will become less and less with distance. It's all about the angle.
Remember our Turning Torso tower?
For an imperfection to block the lower portion of the structure, it has to start out being at least the height of eye/camera, and the further away, the taller it has to be to produce the "cut off." Looking through that pipe, if it's straight and there is no "bulge" due to bending, then for tiny imperfections to produce that lower cut, they must be close to the camera lens. Perspective doesn't magnify the dime when it's far away. To hide the elephant it has to be close to the eye and the elephant at a proportional distance away. (Reminds me of the [urlhttps://www.youtube.com/watch?v=91ahZDmqEQQ]Kids in the Hall skit of the guy threatening "I'm crushing your heads."[/url])
But that's if light follows a straight path. Suppose light is bent or curved upward?
In that case, with the right amount of bending, the dime CAN be further down the pipe and serve as an obstruction. With enough bending you don't even need a dime. The ground itself will be the obstruction as the curved light at a certain angle will not make it to the eye. (Under the right conditions, such upward bending light could cause an inferior mirage.)
That's the concept EAT suggests for the "cut off" effect. Or, if not EAT, the sub-refraction where the air has an inverse density gradient, rarer lower and denser higher.
The weird thing about refracting upward though, is why that would be so universal? Is there an inversion layer in the pipe? Did the increased distance sightings of the Turning Torso just happen to coincide with a meteorological rapid change in the inverted gradient of the air so that the building would be cut off as if earth curvature was doing the cutting off?
But the oddest thing about it is why does it just stop at a given height? If upward bending light is the reason, then the portion of the object above the cut-off would appear stretched, distorted by the still upward bending light, albeit tapering perhaps. Still, as I mentioned with EAT, (and JTolen in his San Jacinto IR analysis affirms), light bending upward would cause a stretching or towering effect on what is left visible, at least near the cut-off. At least with the Tower Torse, the exact opposite is happening. The first few floors above the cut are squashed with the distortion tapering with height above the squash. This suggest light near the cut is actually refracting downward. The sun, too, will "squash" at the horizon as it begins to get cut off. This is explained by refraction bending light downward to follow the (alleged) curve of the earth. If light were being bent upwards, the sun would elongate, not squash.
As for the pipe, I say it's a "bulge" of the pipe bending convex. It may be rigid PVC, but those long, thick PVC pipes aren't so stiff they won't bend a little under pressure or weight. All it takes is a little. It would be easy to check with a laser level.