As η increases, more nanoparticles in the dilute phase or at the interface are incorporated into the bulk dense phase, i.e., a thermodynamic lever rule. This increases the prominence of the bulk dense phase extinction peak around 0.35ω * p , but otherwise does not change the peak location (Figure ) or linewidth (Figure ). The large interfacial area at low η results in pronounced broadening of σ(ω) and notable heterogeneity in cdf(ω res,i ), relative to hardsphere dispersions. On the other hand, most particles are accommodated in the bulk dense phase at large η, and this uniformity produces sharper σ(ω) and cdf(ω res,i ) compared to the corresponding quantities for dense hard-sphere dispersions. Because of the increased local density, the near-field enhancement is more significant in arrested phase-separated materials (Figure ) than in homogeneous colloidal fluids (Figure ). Each particle's hotspot intensity E hot,i is a function of only ω res,i , as all data collected across different η approximately collapses to a single curve (Figure ). Thus, for both homogeneous fluids (Figure ) and heterogeneous gels (Figure ), E hot,i is mainly determined by ω res,i . Including quadrupoles in the optical simulations contributes a constant redshift in the ω res associated with the bulk dense phase (Figure ). Otherwise, quadrupoles have no effect on the extinction lineshape, linewidth, near-field enhancement, or the one-to-one relation between E hot,i and ω res,i .