High explosive anti tank

[T-34type85]

well, i always use HE in IS3 to anti king tiger in a safe distance when i cant flank it or i need to distract it, and it does destroy KING tiger about 6-10 shots of HE. but i dont understand how HE caliber and tank armor determine hull destroy and those damages. i used point blank range 122 on the side Wirbelwind and didnt even destroy its turret but just tracks. so how does HE destroy tanks, like where do i shot? does the more shot on the same area will increase the chance of destroying it? does higher velocity help in Anti tank for HE?