Mixing matrices for different sky coverages. Left panels: Colour plots of the mixing matrix, R_ℓℓ′, computed up to ℓ = 500 with the public code NAMASTER (Alonso et al. 2019). Right panels: Plots of R_ℓℓ^*/R_ℓ^*ℓ^*, centred in three different multipoles, at ℓ = 100 (blue), 150 (orange) and 200 (green). They quantify the mode-mode coupling related to the partial sky coverage, reflecting the blurring of the mixing matrix along the diagonal. The grey shaded regions indicate the multipole range of Δℓ in which we bin our measurements. The top panels are computed from the 10313 deg² region covered by the full PINOCCHIO footprint mask, while at the bottom we focus on the 1004 deg² subregion.