1. A method of optimizing optical parametric models for structural analysis using optical critical dimension (OCD) metrology with an optical metrology system, the optical metrology system including a processor coupled with a memory and an optical metrology tool, the method performed by the optical metrology system comprising: measuring values of far field diffraction signals for a structure, the measurement being performed by the optical metrology tool of the optical metrology system; determining a first optical model fit for a parameter of the structure, the first optical model fit based on a domain of quantities for a first model of the structure; determining a first near optical field response for a first quantity of the domain of quantities and a second near optical field response for a second, different quantity of the domain of quantities, wherein the domain of quantities is a domain of wavelengths, the first quantity being a first wavelength and the second quantity being a second wavelength, and wherein determining the first and second near optical field responses comprises: identifying a region of low correlation of the first optical model fit with measured values for the structure, and selecting the first and second wavelengths from the region of low correlation of the first optical model fit; comparing the first and second near optical field responses to locate a common region of high near optical field intensity for the parameter of the structure; modifying the first model of the structure based at least in part on the common region of high near optical field intensity to provide a second, different model of the structure; and determining a second, different optical model fit for the parameter of the structure based on the second model of the structure.