Scale-independent primordial correlation fraction in the mixed adiabatic and CDI model. The black curves are with Planck high-ℓ and low-ℓ data, while the red ones result from using only the high-ℓ Plik likelihood supplemented with a Gaussian prior on the optical depth. For the 2015 data (top panel) this prior was τ = 0.078 ± 0.019, whereas for the 2018 case (bottom panel) we have adopted τ = 0.055 ± 0.007 from the Planck 2018 TT,TE,EE+lowE+lensing CDI chain.