Analytical as well as experimental height-gain studies for mixed-path groundwave propagation are virtually nonexistent. Therefore, it was shown how the theoretical height-gain for a homogeneous path relates to heterogeneous-path experimental measurements versus height and distance. The results show that the magnitude of a groundwave field which crosses an abrupt boundary rapidly acquires the characteristic properties of the second medium, and the field over a heterogeneous surface attenuates at essentially the same rate as the field on the surface. The groundwave which has crossed an abrupt boundary can be predicted for small heights above the surface by simply multiplying the well-established mixed-path theory for antennas located on the surface by appropriate homogeneous-path height-gain factors corresponding to the local surface impedance, provided the field is predominantly a surface wave.