Simulation of ⟨p⟩ for POL-2 data with N(H₂) > 10²² cm⁻² as a functionof the resolution. The black line shows the relation for the original observations. The blue line corresponds to a case where (Q, U) observed at 20′′ resolutionare taken as a model of the true signal, before adding observational noise and convolving to a lower resolution. The red curve shows the result for data with identical p and I but with a globally constant polarisation angle. The shaded regions show the [10%, 90%] ranges for the random realisations.