In the measured equation of invariance (MEI) method, the accuracy of the MEI coefficients directly affects the solution. Most of the effort is focused on finding the more accurate MEI coefficients. The accuracy of the MEI coefficients is improved by optimization in this paper. The MEI coefficients found by the original procedure are fine tuned to minimize the difference between the induced current on the scattering surface by MoM and MEI methods. One of the stochastic-search methods, the guided random search method, is used. It is evident from the results for scattering by the rectangular cylinders that slight adjustments of the MEI coefficients can reduce greatly the differences between the results of MoM and MEI. It shows that the wave equation can be strictly satisfied by the solutions of the MEI equations if the MEI coefficients can be found accurately, and that the inaccuracy of the MEI method is due to numerical round off errors. At low frequencies, the MoM can help to fine tune the MEI coefficients, which can be extrapolated to the high frequency regions where the MoM is no longer applicable.