I was starting to think it was something about me.
Don't worry, it isn't
I've read Tom Bishop's defense of why lights can appear larger in the distance due to atmospheric effects that counter the usual vanishing point explanation for things getting smaller with distance. But the illustrations he's chosen were streetlights and headlights where focus and optical effects like blooming or glare aren't accounted for.
I feel that by fixing focus, and making filter/exposure adjustments for glare, you can neutralize any blooming and get a sharper edge on the boundaries of the light source.
I could demonstrate how the sun can appear to shrink from a larger intense yellow glow to a smaller, red circle even at solar noon just by applying filtering and adjusting aperture/shutter/ISO. But at a point, the sun stops shrinking (assuming no change to focal length/FOV) and just gets dimmer the more filtering/exposure is applied.
I'm feeling pretty confident that I've captured the boundaries of the sun with my photos to within 1-2%, and that simply measuring pixels is a sound method of comparing diameter of the sun throughout the day as long as the focal point doesn't change. If the sun is moving away from a vantage point on a flat earth along a parallel plane, that pixel width should change markedly in the evening. If there's a magnification effect in play, it's remarkably tuned so that the sun doesn't appear to diminish to a vanishing point but instead remains the same width, even as it appears to sink behind an obstruction.
Not only that, but I can't calculate a way for the sun on a parallel plane 3000 miles above the flat earth to reach a low enough angle to even make it to the apparent horizon. You run out of room. Given the distances involved, the sun should never appear lower than, say, 20° above the horizon from my vantage point before it would dim and recede. It would require an extraordinary amount of refraction (in the opposite direction) or a lensing medium extending low to the surface to make the sun appear 20° lower than it actually is.
And I can't work out a way for the "spotlight" explanation to be true without it manifesting itself somehow in a way we could see on the shape of the sun at sunrise/sunset. I'm really not trying to provoke anyone to defense of their beliefs or to try to convince anyone to change his mind. I'm just trying to understand how this assembly of explanations fit cohesively into a theory of flat earth and how I can test for them. The size of the sun was just one thing I thought I could examine, and I wanted to see if I could detect a change in sun size as would be predicted by a flat earth sun "setting" into a vanishing point horizon. I don't believe I did detect any change, but maybe there's something I missed or a flaw in my method or assumptions. I don't know any flat earthers to ask personally, so I came here (after finding no real FE input on the other community's message board).