A method is provided for optimizing the number of kernels N used in a sum of coherent sources (SOCS) for optical proximity correction in an optical microlithography process, including setting the number of kernels N to a predetermined minimum value Nmin, where a determination is made as to whether an accuracy estimate of calculated intensity is within a tolerable value, and a determination is also made as to whether an added X/Y asymmetry estimate of the calculated intensity is negligible.