Left: difference between the cross-spectra measured using the 20% Galactic mask (20% is the unmasked sky fraction) from that measured with our default 40% Galactic mask. Middle: spectra obtained when differencing the 60% and 40% Galaxy mask measurements. For both left and middle panels and all Galactic masks the same point source and H i masks are used, which removes an additional fraction of the sky. Right: difference between the cross-spectra calculated with the H i-cleaned temperature maps from those with no H i cleaning. This cross-spectrum is thus the correlation between the H i template and the φ reconstruction. The error bars are calculated in the same way as in Fig. 6. Again, the null tests are passed with an acceptable χ².