Michael

Steel will expand and contract uniformly only if it is subject to the same temperature changes.  You have to think of the temperature as a profile through the thickness of the wall.

In winter, the wall will be warm on the inside surface, and cold on the outside surface.  The profile will be steeper on the north side, where it never gets any sun, than on the south side, where it gets some sun.  The profile will also be steeper in areas where there is internal heating compared to those areas (up near the roof or plantrooms or fire stairs) where there is no internal heating.

In summer, the profile will be reversed, with the wall cooler on the inside surface, and warmer on the outside surface.

The slope on these profiles will vary depending on the nature of the materials in the wall section, and the presence or absence of air gaps (cavities).

Clearly, this shows that if the steel is closer to the surface, it is going to be subject to greater temperature changes, and hence greater changes in length, than if it is deeper in the wall section.

The dominance of cracks at corners makes some sense (although not if they are horizontal).  At spandrels, one would tend to think about how the stone units are anchored to the backup structure, and whether there is any possibility of differential movement between the two.

Good luck

david