In-body medical implants are one of the most promising solutions for increasing patient healthcare in the future. Many such devices already exist, however, each new design is a challenge due to size constraints and communication issues which arise due to significant dielectric losses in the body. Therefore, antenna design and placement of antennas in the body is one of key factors for ensuring full functionality of such devices. We address this influence by observing the maximum power density that can be obtained in several in-body scenarios. These results are obtained using simplified spherical body phantom, however, the extracted guidelines can be used in much more complex scenarios and help in achieving efficient antenna design.