Yeah I see what your saying about refraction, and it seems like it could be a major unpredictable variable. But what is plain to see to me is that the island looks like its floating because the water is reflecting the sky... that's the only type of mirage I really understand or have ever seen, I'll have to look into that.
I can't explain every so-called occurrence of "seeing further that we should" but looming, mirages and "Fata Morgana" are very real.
Looming is not that uncommon over water. Mirages are common over hot sandy deserts (and hot roads) but true Fata Morgana are rare.
This might be interesting:
🇮🇹 Fata Morgana Mirage Effect - was originally in Italian.
The big problem is that over water is the obvious place to observe "curvature" but is also a place where atypical temperature gradients are common.
And worse are ice-covered lakes where the ice is commonly colder than the air.
I think a bit of trig should dictate the angle to the top of the visible peak (on flat model), but measuring the angles would be difficult (quite).
Yes and often those angles are very small, only tenths of a degree. 1000 ft over 50 miles sounds a lot but is only 0.2°.