Here's my contribution to this thread (this example is from Australia):
King Island, in Bass Strait, is about 160km from Phillip Island. There is a high point on the northern end of King Island of about 40m. The southern edge of Phillip Island also has high points at about 40m. Yet, if I look towards King Island from the cliffs of Phillip Island, all I can see is a clearly defined line where the ocean appears to meet the sky.
I have never heard of a 40m high wave in Bass Strait, even on a really bad day, so we can rule that out as a possible obscurer of the line of sight. I have also flown on several occasions, and been able to see for distances exceeding 200km, so atmospheric effects are not the cause.
Here's what fits: the earth, according to measurements and calculations, has an average radius of 6,371m. From an eye level of 42m above the surface of the ocean, this gives you a theoretical line of sight distance of just over 23km. Looking for another point at 42m elevation, you could double this to 46km, but that's still not the 160km needed to see King Island. The curvature of the earth gets in the way.
Go on FE'ers, prove me wrong! And I do mean prove, not just say I'm wrong.