Sensitivity of our results to the mPCA contaminant subtraction as function of how many modes have been removed from the original cube. The top panel shows the reduced χ² for each foreground cleaned cross-power spectra relative to its best-fitting model. The bottom panel the corresponding best-fitting Ω_H I b_H Ir values and their 1σ error bars. All quantities are plotted as a function of the N_fg pair of the mPCA analysis, with N_L on the x-axis and N_S colour- and symbol-coded spanning from N_S = 3 in violet to N_S = 10 in yellow. For comparison, the shaded red region highlights the CL23 best-fitting value and 1σ uncertainty, that was obtained with a 𝒯-correction (the ‘uncorrected’ CL23 amplitude would lay between 0.2 − 0.3 × 10⁻³). We highlight in grey the N_L, N_S = 4, 8 results that correspond to our best and reference mPCA result. Results from mSVD and the weighted mSVDw and mPCAw show negligible differences.