Strong differences are detected between the ideal and the actual behaviour of the resistance implemented by an MRC cell. An attempt to deal with these deviations reveals the inadequacy of the widely used BSIM MOSFET model, due to its lack of symmetry when modelling the carrier mobility dependence on the gate voltage. Using instead the EKV model, a nonlinear analytical description for the MRC is presented, rendering a much better estimation of the MRC resistance.