Precise control of spatial distribution of nanoparticles (NPs) within polymeric materials is critical to build nanostructures with programed functionalities. Herein, we systematically investigate the entropy-driven self-assembly of polystyrene-coated Au NPs (Au@PS NPs) and polystyrene-block-poly(4-vinylpyridine) (PS-b-P4VP) block copolymers (BCPs) within a 3D-confined emulsion system. To understand the formation principle of the hybrid particles, four different parameters are examined: (1) the molecular weight of PS ligands (N), (2) the grafting density (sigma) of PS ligands, (3) the size of Au NPs (R), and (4) the molecular weight of the BCP matrix (P). Morphological transitions between alternate-layered onions, seeded onions, and crusted onions are observed by carefully manipulating these variables. To account for these phenomena, we propose a modified swelling ratio (P/N-SDPB) by considering grafted polymers in the semi-dilute polymer brush (SDPB) regime as the only chains available to interact with BCP matrices. This modified parameter successfully explains the structural transitions of the hybrid particles by including the effect of the chain conformation of the grafted polymers on the hybrid particle assembly. Furthermore, the overall Au@PS NP size (d) is considered as a complementary parameter to P/N-SDPB for evaluating the BCP/Au@PS interactions, and together they provide a comprehensive understanding of the hybrid particle self-assembly.