Because I find it particularly difficult to imagine the grand scale of things, I have taken the liberty of making a to-scale drawing of the flat earth.
The scale is 1 pixel = 8 miles. The blue line is the line of vision of someone at the equator on the opposite side of the Earth from the sun looking toward the sun during an equinox. These are the measurements I used, which I found in the FAQ:
Diameter of the Earth: 24,000 miles (3112.5 pixels)
Diameter of the Sun: 32 miles (4 pixels)
Distance to the Sun: 3,000 miles (375 pixels)
None of the measurements are off by more than a pixel or two, due to rounding.

I find it difficult to understand how the sun would appear to even approach the horizon, let alone go beneath it.
Any (serious) answers?