I took "headspace" to mean that with headphones, unlike live performances and speakers, the soundstage goes from left through your head to right, assuming no blobs. To me, it's almost as if I'm laying just in front of the music group. The sound is left to right and mostly eye (or ear) level and above. With speakers, the sound is left to right and out in front of you, like a live performance.
I do agree with your description that good imaging headphones produce a continuous music stage left to right without any blobs and that too many headphones have blobs.