@kerriknox
Youre absolutely right and Im doing my research from both sides, unbiased.
The horizon that you mentioned, I was away on holiday 2 weeks ago and our hotel room was on the 5th floor overlooking the black sea and I kept looking at it on several occasions throughout the few days We were there. But honestly I didnt see any curve and the same goes for the plane journey.
I have even seen independent projects where people send up ballons up in the sky and there is no curveature.
If Im mistaking please do let me know.