At about 3 miles the horizon should form from us, all things being equal. Once the sun gets far enough away from us, and you view it at say a 0.1° angel, the sun will appear behind our horizon.
But the SUN does not start out as small and grow in size, the SUN starts out as the same size it is when it is fully risen above the horizon.. Sun not fading into view, Sun not growing into view .. Sun appears to be rising into VIEW.. Does not grow in size nor does it fade in.. SUN RISES INTO VIEW over what appears to be a CURVED surface
What you have to remember is that the sun is about 3000-4000 miles above us. If you was watching a sun that was at ground level, alongside you, then it should shrink and grow as it moves towards you, or away from you. But since it is so far away from us, it has already shrunk in size, and we will hardly notice much of the size change as the sun moves toward the horizon.
Here is p-brane showing you an orthographic demonstration how the horizon rises to eye level.
HORIZON RISES TO EYE LEVEL ORTHOGRAPHIC VIEW
https://youtu.be/a6mRviXLM-A
At about 3 miles the horizon should form from us, all things being equal. Once the sun gets far enough away from us, and you view it at say a 0.1° angel, the sun will appear behind our horizon.
But the SUN does not start out as small and grow in size, the SUN starts out as the same size it is when it is fully risen above the horizon.. Sun not fading into view, Sun not growing into view .. Sun appears to be rising into VIEW.. Does not grow in size nor does it fade in.. SUN RISES INTO VIEW over what appears to be a CURVED surface
Turns out p-brane has answered and explained the exact concern you bring up.
WHY THE SUN DOESN'T SHRINK TO A DOT on the FLAT EARTH CELESTIAL PERSPECTIVE EXPERIMENT SHOWS why
https://youtu.be/Vq5ixQytLXE
What you have to remember is that the sun is about 3000-4000 miles above us. If you was watching a sun that was at ground level, alongside you, then it should shrink and grow as it moves towards you, or away from you. But since it is so far away from us, it has already shrunk in size, and we will hardly notice much of the size change as the sun moves toward the horizon.