Hi Mark,
I've left you last to reply to because I thought you had the most to say about my experience/s. And, also you appear to know the terrain well. Although, I'm not clear that what you describe is, indeed, so very similar to what I describe. Close enough, perhaps?
Many of my peak or what I would call enlightenment experiences (the vocabulary is different in the Theraveda maps) were similar to what you describe (one even while running). I routinely develop this 360 degree dynamic sphere when I do banishing rituals (I am a Chaos Magician as well as a Buddhist). I suppose the major difference is that I don't have the central ground that you describe. There's only the awareness.
Yes, at any time now, my attention seems to form itself into a container. Yet there is always 'a contained'. And, as described, with prolonged attention that relationship of container and contained begins to reify/thicken up into a very concrete, physical representation. The sense of weightlessness came from feeling entirely suspended within the spherical container of my awareness: that is located at the very center point of the sphere.
Yet, with that weightlessness came a very solid grounded feeling. This is the paradox. What happens when that duality changes nature and really sees itself through? Perhaps only the sphere is left that you, and Stephen Bodian, and Hsuan-sha speak of. That is, if we're all speaking of what can usefully be termed the same thing. I'm not sure.
I wonder where that ground I experience goes? I'd add that in contrast to your own view, I'd say we can 'impute transcendent qualities' to all sorts of things. And quite properly so.
But, yes, you're right, these experiences are not so special. The key is to simply continue exercising attention and follow the sort of cheat sheet Trent offered. These perceptions emerge of their own accord from my practice and they will either continue to deepen and develop in interesting ways, or they will pass, and other developments take their place. Both are fine.