Firstly, one of the points of this thread, which was to point out the pedantic nature of FE arguments, has again been proven by your constant questioning of the term straight line.
Perhaps a more appropriate term which would apply for both FE and RE is a straight line ALONG THE SURFACE. The point is, that one is assuming COMMON SENSE when using the term "straight line". If I were to say to most sensible, intelligent thinking "imagine a straight line on a round earth" or perhaps even better "imagine a straight line on the SURFACE of a round earth", they would know exactly what I meant. That straight line would not "go off into space", because people are using their common sense and knowledge to take into account gravity, which provided one makes no attempt to increase height, means a plane will stay at the same height above the Earth's surface.
FE's arguments are often "Well, a straight line on a sphere would make the plane fly off into space"... Well of COURSE NOT if you use your brains and stop being needlessly pedantic, because you are ignoring gravity, which is always a part of round earth theory. FE'ers often ignore many parts of round earth theory in order to argue against a single point.
On their own, single points can be argued again satisfactorily. For example, if we had no knowledge of anything else, and we just wanted to explain the horizon thing, RE's would say it was curvature of the Earth, FE's would say it is due to mirages and light refraction due to haze from the water (or something like that). That's fine, this makes both sides of the argument equal (although there are probably some physicists who can prove it isn't due to light refraction, I just don't know enough about it).
But when you weigh up ALL the RE arguments against ALL the FE arguments, RE has a lot more credibility, where as FE has a vast number of inconsistencies, contradictions, and holes which cannot be explained because each point has been argued individually, without analysing the whole argument. This can be seen all over this forum.
Again I remind you that I started this thread not to talk about direct substance, there is enough of that elsewhere on these forums. The point, which has been proved numerous times now thanks to the flat earthers that have contributed to this thread, was a pedantic, shallow, and narrow-minded arguing tactic in regards to the subject.