Not from books but rather experience and teachers. Also from noticing subtle connections between different modalities. For instance this mini-chakra happens to be a tapping point in EFT as well as an energy point in accupressure. If I remember correctly I think it was only Sheradon Bryce who called it a mini-chakra. I adopted that term because it was so apt in its positioning within the chakra system and its function as gateway between the third and fourth chakra. Sadly, Google is not a very reliable source in finding esoteric knowledge. I’ve found that to be true time and time again.