A directional antenna pointed in the long-path direction to another station is generally oriented how many degrees from its short-path heading?

Radio signals can travel around the Earth in two directions along a great circle. The 'short-path' is the most direct route to the target station, while the 'long-path' goes the opposite way around the globe. Because the Earth is a sphere, these two paths form a single continuous line. Therefore, to switch from the short-path heading to the long-path heading, you simply turn your antenna to face the exact opposite direction. On a 360-degree compass, the exact opposite direction is always a 180-degree difference. Options suggesting 90 or 270 degrees would point your antenna sideways to the great circle path, missing the signal entirely.