Neglecting reflection can lead to misinterpretation as the actual transmittance alone is suitable when tracking absorbance changes in FP cavities, particularly when the changes are in the same spectral range where the coupling is achieved, as pointed out in an earlier study under electronic strong coupling. Less intuitive is that even when coupling in the IR, such spectral distortions can occur in the visible region where the FP modes are very weak. This becomes significant as the FP mirror reflectance increases. The film thickness used in our study was just at the edge of this onset as can be seen in Fig. We regret to not have identified the underlying reason for the shift in the absorption spectrum and hope that the simulation results presented here will be instructive for the Strong Coupling community. This spectral error does not undermine the conclusion of other published studies showing effects of VSC on London dispersion forces.