1. A method of improving lithography system imaging performance, the method comprising: obtaining reference values of, or for, a reference lithography system, the reference values at least in part defining a desired imaging condition of a target pattern; performing, by a hardware computer system, an imaging simulation using a model of another lithography system and the reference values to arrive at imaging results; and based at least on the imaging results and measured results from a substrate exposed using the other lithography system, varying, by the computer system, parameters of the other lithography system such that values of the varied parameters of the other lithography system enable the other lithography system to realize, as a best match or within a predefined error criteria, the desired imaging condition of the target pattern.