Distinguishing contributions of physical and optical characteristics, and their interactions, to complicated features observed in spectra of nanocomposite plasmonic systems slows their implementation in optoelectronics. Use of vacuum, effective medium, or analytic approximations to compute such contributions are insufficient outside the visible spectrum (e.g., in energy harvesting) or for interfaces with complex dielectrics (e.g., semiconductors). This work synthesized discrete dipole computation of local physical/optical interaction with coupled dipole approximation of far-field Fano coupling to precisely distinguish effects of locally discontinuous dielectric environment and structural inhomogeneity on complicated spectra from a square lattice of gold nanospheres supported by complex dielectric substrates. Experimental spectra decomposition of resonant energies/bandwidths elucidated indium tin oxide affected surfaced plasmon resonance while silica affected diffractive coupled resonance features. Energy transport during plasmon decay was examined for each substrate under a variety of physical support configurations with the gold nanospheres. The compact, multi-scale approach can be adapted to arbitrary nanoantenna shapes (e.g., nanorings) interacting with various dielectrics (e.g., dichalcogenides). It offers >104-fold reduction in computation time over existing descriptions to accelerate the design and implementation of functional plasmonic systems.