Sri Ramana Maharshi said that he gave the location of the Heart in the right side of the physical chest for those who were still identified with their body. He was clear that in absolute reality our mutual One-Self cannot be located, limited, or confined to a single place in the body.
The principle of the "witness" (or observer) who is aware of the entire realm of human experience, is well-known in spiritual circles and the worlds of meditation and mindfulness. At first, for many people the witness takes the form of a mental concept, which, although not the whole truth, is a step up in consciousness.
Self-inquiry differs from all other meditations that I'm aware of because all the others require us to dedicate a period of time to their practice, need a quiet place, entail closing our eyes, and demand the removal of external distractions to be fully effective – or even able to be performed at all.