I was always under the impression that it was generally considered that SBW II was a tongue blocker, but I also seemed to think he was puckering when watching video footage... maybe it's just hard to tell. Perhaps the tongue block police can clarify.
Too many people are asking me to explain my Sonny Boy comment. Here is the reference......
I notice that Sonny Boy is not "Puckering", but is relaxed with harmonica resting on his lips like a glass of water and inhaling/exhaling.
The Iceman