Two-component aggregative mixing of initially bidisperse particle populations results in a Gaussian-type compositional distribution function, which can be fully described by the overall mass fraction of component A (phi) and the mass-normalized power density of excess component A (chi, indicating the mixing degree). chi will reach a steady-state value once the selfpreserving size distribution is attained. The relation between the steady-state value of chi (chi(infinity)) and its initial value (chi(0)) has not been investigated before. This paper applies population balance modeling to gain insight into the dependence of chi(infinity) on initial feeding conditions. By model fitting from hundreds of systematically varied simulations, it is found that chi(infinity)/chi(0), which depends on phi, can be formalized by the Gaussian-type function for Brownian aggregation in the free-molecular regime as well as in the continuum regime, however with different geometric standard deviations. The present work can help to optimize mixing by properly selecting the initial mass and number concentrations of components A and B in the feed.