The useful model: The E region lies above the D region and can refract lower HF signals; localized dense patches can also create Sporadic-E propagation into VHF.
What controls the result
Ordinary E-region ionization follows daylight and can support shorter HF hops. Sporadic E is a distinct, patchy mechanism with rapid geographic and frequency changes.
The misleading shortcut
Calling every short-skip opening “E skip” ignores F-region geometry, NVIS, scatter, and the difference between ordinary E and Sporadic E.
Make the better decision
Compare distance, band, time, ionosonde traces, and VHF beacon reports; use the mechanism as a working explanation only when the observations fit.
Evidence boundary
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.
