I have been a believer in the things Bigger (bib) has written on hanging and his thoughts because he has been so instrumental to PE (not to mention his design if his hanger). His idea of heat and hanging is to heat the first half of the set to help the stretch then let it cool in the stretched state during the second half.
As for the ligs or the shaft, if you are hanging BTC then heat the ligs. If you are hanging OTS then heat the shaft. It probably doesn’t really matter as long as you use heat when hanging. If you do a search you will find plenty of info on this written by him.
I should have been more clear in my post I made because I have been hanging BTC.