I wrote to the AAI too, and they have intimated that as per the CAR on All Weather Operations, the Operator has to set their visibility minima, which must be approved by the DGCA. I checked from an IndiGo pilot, who confirmed that this is indeed the case.
That will work for scheduled operators, who operate all over the country or even non-scheduled aeroplane operators. But this wouldn't work for helicopter operators, who fly IFR only once in while and that could be anywhere in the country!
So now my next question: Jeppesen shows a visibility minima on the charts that we (I fly with a non-scheduled operator) follow. Where does Jeppesen derive this minima from? And how does it become legal, since it is not expressly approved for us?