Numerical dosimetry is an essential procedure in designing and optimizing propagating EM-devices that confirm to the recommended limits of Specific Absorption Rate (SAR). However, as frequencies go higher, the complexity of the computational problem increases substantially. Moreover, the high heterogeneity of the human body and the uncertainty in its tissues properties add to that complexity. Furthermore, as the numerical domain becomes very large, the impact of numerical dispersion becomes more visible leading to decrease the meshsize even more. This article sheds some light on the 3D -simulation of such computational problems, and revisits the necessary mesh-size condition that ensures convergence and accuracy of results. Comparisons between FIT and TLM methods are presented to show the speed of convergence for both methods.