In visualisation meditations, I don’t know “where” to look

Sometimes I wonder whether I should be looking “down” from my eyes, through my neck and into my chest… or if my “eyes” should themselves move to the chest … or… something else?

Your physical eyes should almost always never move. The visualization should occur in your mind's eye only. Unfortunately, it's a very common problem that the physical eye tends to wander where your mind's eye is, this is just due to habit and conditioning. The more you practice, the more it will subside. You could also do short sessions of anapanasati/breath meditation or other practices where the object is not visual, just to train your mind not to use your eyes and focus on some sensation-based object instead.

There are meditations which do not involve any kind of visualizations at all, and I would encourage you to try those for a change. For example, look for Vipassana meditation, which fabricates nothing, and asks you to do absolutely nothing, but just to notice what is there.

You have probably heard of it even if you are not already aware of the name - it's the classic "close your eyes and watch your breath" meditation, at its core.

If you wish to scan your body, then let your attention or awareness move from the breath onto the other body parts. Especially if a body part requires your attention, for example due to pain, itching, tension and so on, just be very aware of it and really "allow" and sense the sensation, no matter if it's positive or negative. Do not try to suppress anything. If you wish to move on, gently move your attention somewhere else (can also be sounds or other senses if there are any), and if you find nothing of interest, go back to the breath.

If you ware not sure what it means to be "aware" of something, one hint is to simply tell yourself what you are aware of - for example, in your mind, "speak" to yourself "breathing breathing breathing" or "itching itching" or "tense stomach tense stomach" or "hearing car hearing car" or whatever it is.

The only special thing about the breath is that it is always there, so it's an easy anchor point.

Fun side fact: Aphantasia is the inability to voluntarily create mental images in one's mind. I have that. If I close my eyes, I can not make any image or object appear in my mind. It does not matter if it's an apple or an "energy ball" or whatever meditation object you want to use; it just does not happen. I do not know if this is related to your meditation problem, just wanted to bring it up.

It's possible to move the attention eye (inner eye) around and through the body without moving the eyes, and if you get good at it, maybe you can read the print on a newspaper several yojanas away.

Also, what you seem to perceive as trouble trying to conceptualize a body - in which your confusion centres around location, distance and space - could actually be used positively. Maybe some formless practices might prove fruitful like the arupa ayatanas starting with the investigation of space, how space occurs in conjunction with form and how you seem to move through space - which all lead to the exposure of your inner-world version of space, which is to say lacking. This can be investigated even off the cushion.

Moreover, Dzogchen and his pointing-out instructions might be useful and maybe ponder this Zen koan which points to the intangible essence of who we are:

Show me your Original Face, the face you had before your parents were born.

To focus on the main contention of your question: it is extremely practical to find some kind of body awareness during meditation and since you have an attachment to the eyes, then the facial region is where you should try to expand your attention. It shouldn't feel strenuous, but since the mind has been clinching for so long, relaxing the attention might feel unfamiliar and even uncomfortable, thus evoking confusion. That's probably what you're trying to work through at the moment.

This is more like a general comment than an on-point answer... You know why you're having this problem?

Because visualization is a kind of fabrication. You're creating the experience, assembling it from the elements (signs) available in your memory.

As you fabricate the seen you're trying to fabricate the seer and are struggling at that. Which is kind of ironic, because you have the very duality of subject/object right in front of your eyes and yet are looking for something more mundane than this immaculate insight.

Imagine if you succeeded at fabricating a nicely localized seer (aka the point of view) of these experiences. Now, think about that which is seeing the seer. From what perspective is it looking at it?

It's like that fictional story, a captive-born bird was told it needed to exercise its wings for something called "flight" it had never known, and it was complaining that the exercises were getting difficult due to the lift created by the strengthening wings. It seems to me you are having the same problem, my friend.

If I were you, I would reevaluate my practice and see if maybe I need to turn the page in my meditation handbook and practice the next thing.