I think groundwave propagation only happens reliably at the extreme low end of the HF spectrum, and is mostly associated with medium and long waves (160m ham ba

I think groundwave propagation only happens reliably at the extreme low end of the HF spectrum, and is mostly associated with medium and long waves (160m ham band & AM radio for example). For most of the HF spectrum reflections off the ionosphere are the main useful propagation mode. At the short end (like CB radio) bouncing of the ionosphere is harder so line-of-sight is more common.