Difference of the ratios rr_01/10(n) as a function of frequency between the standard model (no PC, ξ = 0.0) and (i) the model with PC with an extent of ξ = 1.3 (red continuous line), (ii) the observations (black). The dashed red line is a sinusoidal fit of the red curve (see text). Note that to calculate the differences, models were splined on the observed frequency grid. A detailed comparison with observations is provided in Fig. 4.