We further tested the model by investigating particles with different sizes and therefore with different coupling energies ℏΩ 0 . In the purely classical approach, we expect the additional peak to be more pronounced for smaller particles as the relative amount of excitonic material rises. These effects are also observed for the simple model of a Drude sphere with a Lorentz shell (see Supplementary Information). On the other hand, smaller particles support larger coupling strengths. Consequently, when applying the HQM for decreasing particle sizes, the (classically larger) rogue peak is suppressed by a more pronounced power broadening. In addition to the analytical Mie-Gans calculation, we also used a numerical FEM solver to determine whether the exact particle shape influences the outcome. In both calculations, we used the particle dimensions as determined by TEM and simulated the bare nanoparticle spectra (see Supplementary Information). Moreover, we used the same parameter set for TDBC as indicated above, except for Ω 0 , which we varied according to the measured mode splittings. The upper row in Figure presents measured (orange lines) and calculated spectra for particles with a transverse diameter of 11 nm, 18 nm, 34 nm, and 37 nm, using a vacuum Rabi splitting Ω 0 of 100 meV, 85 meV, 77 meV, and 65 meV, respectively. The agreement between measured spectra and model is remarkable. Mie-Gans (dash dotted blue lines) and FEM simulations (dashed dark blue lines) are consistent, no shell resonances appear at the positions of the "bare" dye and in all cases, the peak splitting is very well reproduced. The slight mismatch for the smallest particles is probably caused by the increased surface damping in such small particles, which modifies the permittivity of gold and is not considered in our model.