For some engineering scaling reasons small things tend to be pretty tough in proportion to their size; supposedly the core arrays in the space shuttle Challenge

For some engineering scaling reasons small things tend to be pretty tough in proportion to their size; supposedly the core arrays in the space shuttle Challenger survived ocean impact and were readable once recovered. core was relatively sensitive to temperature and the currents had to be varied to match the temp for optimum performance. Which can be worked around as OP did by not optimizing for minimum power or minimum error rate. Also the more cores the sense wire ran thru the more temperature sensitive the core became.