Unconventional computing may overcome some of the limitations of traditional silicon-based systems using alternative materials and computational mechanisms. However, due to their complex underlying dynamics and high-dimensional parameter space, the design of these materials such that they perform computation is non-intuitive, making AI-driven design attractive. It has been shown that evolutionary algorithms can tune the structural properties of grains within a granular material such that it computes logical functions. In recent years, programmable granular metamaterials have been developed so that multiple physical properties of individual grains can be altered independently. This raises the question of whether allowing evolutionary algorithms to tune more grain features within a granular material frustrates or facilitates its ability to embed computation. In this work, we show that the latter is the case, when grain sizes and stiffnesses are co-evolved to embed Boolean logic gates, compared to evolving just sizes or stiffnesses alone. We report physical verification of evolved designs, taking a further step toward the provision of alternatives to electronic computing.