Silica-polymer metamaterials are one promising candidate of radiative-cooling materials suitable for scalable manufacture. However, the strong coupling between the silica and polymer components and their respective contribution to total emission remain unexplored. In this work, we developed a 3D full-wave model for such a randomized composite system to retrieve the spectral emissivity of individual components and uncover the interacted physical mechanisms. The results demonstrate and decouple the cooperative emission in the scatter-medium system and quantitatively evaluate the geometry-dependent light-matter interactions, which sheds more light on silica-polymer metamaterials and provides helpful guidance for designing similar thermal-control materials.