Antennas, and more generally any equipment under test (EUT) capable of coupling to impinging electromagnetic waves, are well-known sources of power loss in reverberation chambers (RCs). As such, it is fundamental to model their contribution to an RC quality factor. The standard model available in the literature is based on power dissipated in loads connected to an antenna. This paper argues about the inaccuracy of this description, where internal dissipation within an antenna (or EUT), associated to potentially low radiation efficiencies, is neglected. An alternative model is validated by showing its self-consistency in predicting change in loading effects as opposed to the standard model. It is expected to have practical importance for tests performed in the low-frequency range of RCs, where antenna-related dissipation is the dominant loss mechanism, and in particular for EUTs which can be expected to display poor radiation efficiencies.