At present time, numerical dosimetry has reached a certain maturity and dedicated commercial software exist. However, fast and accurate characterization of exposure in real condition is still challenging, among other reasons, because the exact posture of the “victim” has to be taken into account. The classical approach is to estimate the source magnetic field and then to perform a dosimetric computation with a postured phantom. We propose a different approach, based on a change of variable, which takes the postured phantom to a not postured one. We demonstrate that this procedure ends up in a change of tissue conductivity, which is localized in knees, elders and other articulations, where deformations due to posturing are large.