This is exactly what I experience. The only time I perceive anything like "seeing in the mind's eye" is on the edge of sleep and it vanishes if I pay any attent

This is exactly what I experience. The only time I perceive anything like "seeing in the mind's eye" is on the edge of sleep and it vanishes if I pay any attention to it. (I do see in dreams, which is distinctly different from the hypnagogic imagery.) I usually describe what you refer to as a sense of space on a monochrome model as being as if I've loaded a JSON file listing out all of the points on a 3D model, but there's no renderer to view it with.