is it all just made up for shits and giggles?
Nope, it's not made up. If the earth were round the sun really would be triangulated to a distance of 93 million miles. The angular size in the sky would give it a large diameter for its distance as well.
Now, if we use those same exact triangulation equations under the assumption of a Flat Earth, the sun becomes much closer and much smaller. By necessity, since astronomers gauge a celestial distance by studying the angle of an object in the sky from two separate points on earth and compensating for curvature, the shape of the earth is intimately attached to the distance of the Astronomical Unit.
You are triangulating to measure the size to the sun but you are forgetting that the distance to the sun, in your FE model is not constant!
If you assume that the height at which the sun hovers is 1 (we will measure everything in UA's to make calculations simple), then the distance to the sun (d) with respect to the altitude (a) (altitude is the angle from the horizon to the sun, in this case) is:
sin(a)=1 / d
Moving terms around, the distance to the sun in UA's is:
d = 1 / sin(a)
Assuming the apparent size of the sun is 0.5 degrees when the sun is exactly at the zenith, (an important specification if we are talking FE), and since the apparent size of the sun (s) is inversely proportional to the distance (d), we have:
s = 0.5 * ( 1 / d ) = 0.5 * sin(a)
Therefore, if the sun is at an altitude of 30 degrees, for example, the apparent size would be 0.25 degrees. If the sun is at an altitude of 10 degrees, the size of the sun is down to just under 0.1 degrees.
But, surprise, surprise, the apparent size of the sun is always close to 0.5 degrees, or about the size of your thumb's fingernail when you extend fully your arm.
In conclusion, triangulation would positively show that FE proponents are right if only the sun was seen smaller as it approached sundown, but the opposite is true.