Comparison between diagonal and non-diagonal errors on the real-space angular power spectrum, C_ℓ, in different redshift bins. Grey squares and magenta pentagons are measured from the set of mocks, with the full PLCs sky coverage and with its 1000 deg² subregions, respectively. The black lines are computed through the Limber approximation, with the diagonal $1/\sqrt{f_{\mathrm{sky}}}$ boost factor. The purple lines account for the mode-mode coupling induced by the mixing matrix, R_{ℓ, ℓ′}. Solid lines refer to the full PLCs sky coverage, while dashed lines refer to 1000 deg² subregions.