What controls the result
For HF, useful propagation comes from the combined behavior of altitude regions rather than hard mirrored layers. Electron density, collisions, Earth’s magnetic field, time, season, latitude, and solar activity all change the path.
The misleading shortcut
The “radio mirror” picture is convenient but misleading: a signal is normally bent through a changing medium, and the path may be absorbed or scattered before returning.
Make the better decision
Use ionosonde and space-weather data as a live model, select a band with margin, compare several paths and takeoff angles, and let signals actually heard override a generic forecast.
Propagation and antenna metrics are meaningful only with their frequency, path, geometry, reference plane, loss assumptions, and measurement method. Use current observations and the exact installed system.
