Map of the RRM excess for various cutoff limits of H I column density and Hα intensities to illustrate the variation of σ_Excess. We retained excess values when both subsamples (with and without Mg II absorbers) contained a minimum of 100 sightlines. The vertical green and horizontal blue lines mark the thresholds H I = 3.5 × 10²⁰ cm⁻² and Hα = 1.0 R, respectively, which we adopted to compute the values reported in the Table 1. The statistical significance heat map is shown in Fig. C.3.