Under the normal incidence condition, 𝑘 VSC will peak at 𝜔 c = 𝜔 0 . For the 1D cavity case, 𝑘 VSC naturally reduces to the single-mode case (Eq. 32), and we have directly compared the FGR analytic expression with the numerically exact rate constant for a single molecule under strong coupling, which provides agreement across a range of light-matter coupling strengths and cavity frequencies. For the 2D cavity case, we evaluated the FGR rate expression (Eq. 35), and found a similar sharp resonance at 𝜔 c = 𝜔 0 compared to the single mode (or the 1D case), with an asymmetric rate constant profile and a long tail when 𝜔 c < 𝜔 0 . This is a unique prediction from the current theory, which should be checked with future experiments.