A method is provided, including: forming an optical computing device having a first plurality of sensing elements selected to measure a characteristic of a sample, generating a transmission function from a first add-on integrated computational element (ICE), and evaluating, with a merit-function and the transmission function of the add-on ICE, a predictive performance of a modified optical computing device that includes the add-on ICE in addition to the first plurality of sensing elements. Also, modifying the first add-on ICE to improve the predictive performance of the modified optical computing device according to the merit-function and a modified transmission function of the add-on ICE.