Jackknife robustness test performed by dividing the eBOSS and LoTSS masks into ten subregions and computing the eBOSS × LoTSS angular power spectrum for the first redshift bin, 0.6 < z < 0.66, using a leave-one-out approach. It illustrates the 10 α measurements along with their associated 68% confidence interval as a function of their reduced χ² values (light blue points). The black pentagon represents the α measurement obtained from the real data measurement using covariance generated from FLASK mock, corresponding to Case 1 in Table 1. The blue pentagon represents the result using 1000-subregion jackknife covariance with real data measurement.