I'm not sure if this will answer your question, but it may help to answer some part of it.
Imagination is created by your mind, using information from your memory.
Clairvoyance or 'seeing through the eyelids' is seeing something that is actually there, be it its energy or its physical presence.
When I 'see through the eyelids' (I call it etheric vision) I am seeing the physical world around me or part of it. I'm not sure what with. Maybe my etheric body, maybe another perceptual organ.
When I do Robert's exercise, I see a fuzzy representation of what's there. I'm not seeing it in my mind's eye, I'm seeing it with my eyes, and possibly with another perceptual organ.
When I imagine I'm eating an orange, and imagine it, I'm seeing it in my mind's eye. The orange isn't there in front of me, it's an evoked memory which I then use to get a feeling.
I hope this helps.