In a recent lecture, Koun Franz recommended letting the mind move away from the head as an experiment:
Okay… So, have your hands in the cosmic mudra, palms up, thumbs touching, and there’s this common instruction: place your mind here. Different people interpret this differently. Some people will say this means to place your attention here, meaning to keep your attention on your hands. It’s a way of turning the lens to where you are in space so that you’re not looking out here and out here and out here. It’s the positive version, perhaps, of “navel gazing.”
The other way to understand this is to literally place your mind where your hands are–to relocate mind (let’s not say your mind) to your centre of gravity, so that mind is operating from a place other than your brain. Some traditions take this very seriously, this idea of moving your consciousness around the body. I wouldn’t recommend dedicating your life to it, but as an experiment, I recommend trying it, sitting in this posture and trying to feel what it’s like to let your mind, to let the base of your consciousness, move away from your head. One thing you’ll find, or that I have found, at least, is that you can’t will it to happen, because you’re willing it from your head. To the extent that you can do it, it’s an act of letting go–and a fascinating one.
(“No Struggle (Zazen Yojinki, Part 6)”, by Koun Franz, from Koun’s “Nyoho Zen” site: https://nyoho.com/2018/09/15/no-struggle-zazen-yojinki-part-6/)
I’d like to say that I too find it fascinating, and add something from my own writing:
Just before I fall asleep, my awareness can move very readily, and my sense of where I am tends to move with it. This is also true when I am waking up, although it can be harder to recognize (I tend to live through my eyes in the daytime, and associate my sense of place with them). When my awareness shifts readily, I realize that my ability to feel my location in space is made possible in part by the freedom of my awareness to move.
I sometimes overlook my location in space because I attach to what I’m feeling, or I’m averse to it, or I ignore it. The result is that I lose the freedom of my awareness to shift and move, and I have difficulty relaxing or staying alert. When I allow what I feel to enter into where I am, then my awareness remains free, and I can relax and keep my wits about me.
As to the implications for zazen, I find that what I feel in my senses and beyond my senses bears against my location of mind like the left hand bears against the right, and yet it’s all about letting go.