The useful model: foF2 is the highest frequency returned vertically by the F2 region at an ionosonde under the measured conditions.
What controls the result
Oblique paths can support frequencies higher than foF2 because they meet the ionosphere at a shallower angle; path prediction converts vertical data into an estimated MUF.
The misleading shortcut
Treating foF2 as the global maximum usable frequency ignores geometry and the fact that one ionosonde samples one place and time.
Make the better decision
Use the nearest representative ionosondes, watch the trend rather than one point, apply an oblique-path model for the endpoints, and validate with signals on adjacent bands.
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.
