Fundamental radiation limitations of in-body or implantable antennas should give us an estimate on the feasibility of some desired system. It was shown that near-field effects and distance to the body - freespace boundary are critical aspects, while the shape doesn't play a major role in the achievable power. Through the frequency analysis of these limitations in this paper we provide another perspective and show how rigorous and approximate approach to near-field and reflection losses manifest in the results. This is demonstrated on a spherical body example which contains a small spherical implant which can he placed at different positions within the body in order to simulate different implant depths. The results reveal that reasonably accurate description of in-body loss mechanisms can be achieved using our previously defined fundamental radiation limitations for power density, however, depending on the frequency different loss aspects must be treated with special care.