Yes, what you said.
I saw Carlos at the Bill Graham memorial free concert, which was an all-day all-star show in Golden Gate Park. Most acts came out onstage and did a quick set, but Carlos first did a sound check. He carefully placed bits of tape on the floor where the desired effects could be made due to amplifier feeding into the guitar at various locations. He appeared to control it easily.
Joe Satriani gets some marvelous feedback effects that are dependent on stage location, and you can watch him on some of the YouTube videos, moving around to find the sweet spots for certain harmonics. No tape -- he's too cool to use tape -- but he mentally notes where the zones are and returns at will.
That Golden Gate Park was a hell of a show. The Dead played a set with John Fogarty..