We had white paper talking about the sensor fusion especially the magnetic calibration and compensation.
SIC (soft iron matrix compensation) is one of the topic inside. And calibrate the SIC, need some special test equipment like 3D coil to generate defined magnetic environment.
Hope you can get more idea from this document.
In generally, SIC is compensate the soft iron from the device which related to design and material selection. So you can measure it in the lab and compensate it in the design phase. Then in the real device geography position, the sensor need to understand the magnetic environment surrounding, That is the reason user need to do manual calibration.