1. A method of optimizing optical parametric models for structural analysis using optical critical dimension (OCD) metrology, the method comprising: determining a first optical model fit for a parameter of a 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; comparing the first and second near optical field responses to locate a common region of high optical field intensity for the parameter of the structure; modifying the first model of the structure 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.