How does the ionosphere affect radio waves with frequencies below the MUF and above the LUF?

The Maximum Usable Frequency (MUF) is the highest frequency that the ionosphere will bend (refract) back to Earth for a given path. The Lowest Usable Frequency (LUF) is the frequency below which signals are entirely absorbed by the D layer. When a radio wave's frequency falls precisely in the 'sweet spot' between the MUF and the LUF, it avoids being lost to space and escapes complete daytime absorption. Consequently, these waves are successfully refracted by the F layer back to Earth, making reliable long-distance 'skip' communication possible.