The actual representation as practiced today per hai di zhen (needle at sea bottom) is literal where right hand is going downward where a logical explanation is hand going towards qihai/dantian (groin) or lower, whicn may not be actual use. It apears most people only know about this literal explanation so in this sense, it has reality (albeit its own).
The metaphor is that the "sea bottom point location" may have been "lost" meaning no one may be aware of its actual position, or, it has roots in classical "Daoist" acupuncture, or even modern acupuncture for that matter i snot discussed-I do not know.
I will not venture to say it is "secret"-only that people do not talk about it openly.
My last two statements follow each other like night and day, wherether they mean the same thing is left to the wind.
All I am saying is the common meaning (what most people say it is) is distinct from its physical "esoteric" reality, though they may share a common thread.
At this point I cannot prove my asertion on location but I will try in the near future to give a reference for you to check since your Mandarin ability far exceeds mine.