Oh and BTW, if you’re good at it, by subtly changing how you position the guitar relative to the amplifier, you can alter the relative amplitude of the various harmonics, and get the note to shift up one or even two octaves, and come back down. It’s a gorgeous effect, and doesn’t require any electronics other than lots of gain, although overdrive can be helpful in smoothing out the transitions.
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.