On a sunny day (26 Sep 2006 05:33:33 -0700) it happened "Telstar Electronics"
wrote in
.com:

LeIand C. Scot wrote:
Tacking the diodes on to the case of the transistor works better than
attaching them to the heat sink due to the relatively slow thermal response,
the heat sink changes temperature slower than the cap on the transistor.

That's simply not true... while the heat sinks response might be a bit
slower... it's a much better indicator of the temp of the transistor
die. The ceramic cap on those transistors will overshoot the die temp
in both directions

This is not correct. there is no 'overshoot' in temp possible.
Unless you know how to heat solder to 250C with a 200C soldering iron?
An other Telstar miracle ;-)?
The thermal response will be faster, resulting in better protection.
A slower response could result in reducing current too late.