Same relationship as shown in Fig. 6, but limited to data in the common field-of-view of SDO/HMI and SO/PHI, which falls between 0.05 < μ < 0.75. Consequently, the orange curve now uses much less data than that shown in Fig. 6, and therefore has more limited statistics, but it is calculated in the same way as the one in Fig. 6. The green curve (double-viewpoint approach) remains unchanged. An additional blue curve is included, representing the facular contrast derived from both I_c and B_LOS measured at the limb, but using pixels selected from the facular map derived at disc centre. Markers and shaded areas have the same meaning as in Fig. 6.