F3 ??? let alone F4 layers.
Quite believe during solar cycles and earths magnetosphere is effected by the cycles and it too has its ups and downs. like in increased solar cycle the mag is increased like adding or making the filter stronger and weakens during lower cycles of the sun
But not explain how our radio waves can effect it on its reflection back to earth is it to high to allow bouncing back signals to reach hearth and not simply bounce back past it like skimming off the earths atmosphere. Just goes to show we don’t have a full understand of our ionosphere as yet.