The disclosure is directed to improving optical metrology for a sample with complex structural attributes utilizing custom designed secondary targets. At least one parameter of a secondary target may be controlled to improve sensitivity for a selected parameter of a primary target and/or to reduce correlation of the selected parameter with other parameters of the primary target. Parameters for the primary and secondary target may be collected. The parameters may be incorporated into a scatterometry model. Simulations utilizing the scatterometry model may be conducted to determine a level of sensitivity or a level of correlation for the selected parameter of the primary target. The controlled parameter of the secondary target may be modified until a selected level of sensitivity or a selected level of correlation is achieved.