Despite the undoubted versatility and effectiveness of the finite-difference time-domain (FDTD) method and its enhancements, there remain some problems which require more computer power than is practical. An example of such a problem is the coupling between two or more tilted antennas in the presence of a scattering environment such as is encountered in a body area network (BAN). The dual challenge of a wide range of scales and complicated structures which are not aligned with a Cartesian mesh are addressed using a novel Time Domain Huygens (TDH) approach. Results and comparisons with measurements are presented showing the effectiveness of the method. In addition, the measured and predicted variations of BAN propagation characteristics with body size are investigated.