A response from dadoonet the great : I feel very flattered 
....
.. and it is fully accurate as ever.
nested fields seems the definitive solution.
Since it has been marked as evil for performances , I never looked into it, but here, I have no choice.
With that in mind, I did a new research and found this previous issue:
(How to search Multiple dense vector fields, including nested filelds)
Everything is in it. mine is a poor duplicate.
Thank you, you both, for your valuable help.
Please close.