Thanks for your reply.
I have been looking for vunerable spots in the Sherman online at tank town (all very short range ambushes, and all with T34 HVAP). So far I've found that hits to the turret, sloping front armor, or track don't do anything. Two spots that will kill the Sherman with one HVAP are hits to the middle of the rounded front hull armor and hits to the vertical rear. Again, this is at point blank range in town.