I second cadaveca too.
Your results are not that abnormal. CPU temperature is anlog reading somewhere on the die, between the cores. Removing your IHS also suerely makes your CPU readings no more reproductible with other CPUs.

It is just normal, that the more you increase the load/heat on cores, th emore they get hot while CPU temperature will increase in a slower manner. This is just normal physics, as the source of the heat is the cores where DTS sensors are, while CPU temperature is far away from the cores.

Personally, I'm not shocked by your results. Even without removing the IHS, the linear relation between coretemp (deep temp) and IHS temp (superficial temp) is lost on high OC.

But, other reports on DTS sensors being freezed is more than abnormal.

What you could do is use a temp sensor and put it on one core, and another on the CPU die. You'll see that they confirm the non linear relation