A sub-region of the first dataset in this study (same as in Fig. 4), showing the facular map determined at disc centre by SO/PHI-HRT and reprojected onto the reference frame of SDO/HMI. After re-projection, an additional selection criterion is applied: only those facular pixels are kept, for which the reprojected B_LOS/μ, originally measured at disc centre, exceeds three times the noise level of SDO/HMI at the limb. Pixels meeting this criterion are shown in colour B, while those excluded from the analysis are shown in colour C.