Sub-region of first dataset pair in time series used in the study, showing B_LOS derived from the limb observation by SDO/HMI (first panel), the same data divided by μ (B_LOS/μ, second panel), and B_LOS derived from disc centre by SO/PHI-HRT; these are divided by the μ value of the disc-centre view and re-projected to the limb to match the reference frame of SDO/HMI (third panel).