@ Boots,
Oh c'mmon, all your GE-based arguments and proofs have been overused already. I suggest you read also ALL FE arguments and facts re such topic. Anyway, let me tell you that in those lines of arguments, both GEs and FEs have valid points, only that they don't see that, causing them to pointlessly and endlessly argue and argue without getting to the truth out there. Don't get into such trap, you might find yourself knowing nothing but shallow info. Be a truth seeker. Find out there somewhere an irrefutable and indubitable proof(s)... Thanks. 
Well, Flat Earthers claim that
the horizon always rises to eye-level, no matter what the elevation.
Basic Perspective
A fact of basic perspective is that the line of the horizon is always at eye level with the observer.
. . . . . . . . . . . . . . . . . . .
"Anyone who has ever been to the seaside will have seen a horizon (as long as it wasn't foggy). This is the line you see far away, out to sea. It's the line where the water stops and the sky starts. There are horizon lines everywhere, but usually you don't see them because something like a hill or a tree or a house is in the way.
You always see the horizon line at your eye level. In fact, if you change your eye level (by standing up, or sitting down) the horizon line changes too, and follows your eye level. Your eye level always follows you around everywhere because it's your eye level. If you sit on the floor the horizon is at your eye level. If you stand up, it's at your eye level. If you stand on top of a very tall building, or look out of the window of an aeroplane, the horizon is still at your eye level.
This is made as a direct unsupported ststement in
the Wiki.
Well, I claim that on a globe there is a measurable, though small, angle of dip to the horizon from the local horizontal. Surveying instruments can measure this from quite low elevations and much less precise levels can detect it from around 300 m elevation and higher.
I have made numerous posts on this and had little response, other than "I can't
see any curvature", but I am not talking about
curvature at all. Here are some of those posts (all much the same):
Re: Why can't we see the sun via telescope after it sets/moves further? or can we? « Reply #18 on: September 14, 2016, 02:16:28 AM »,
Re: It shouldn't be that hard to settle whether the earth is round. « Reply #8 on: August 30, 2016, 12:53:12 PM »,
Re: eye level flat horizon at 120,000 feet « Reply #18 on: September 21, 2016, 07:16:25 AM ».
The only reason for quoting more than one is so you can read any comments or objections others have made.
But I believe that "Dip Angle to the Horizon" measurements done from a number of different high elevations (up to say 10,000 m) is enough to decide whether the earth is f;at or a globe.