I would suggest 1 on 1! or maybe standing between 2 shooters...if the SSAA consider 12 shooters to be adequately supervised...
The law refers to 'immediate supervision', so if the supervisor (who can be an RO or anyone with an appropriate licence) is 4 shooters away instructing Johno on how to properly shoulder the rifle.... then he couldn't possible be immediately supervising Davo, 4 benches away.
Firearm Act 1996
SCHEDULE 3
NON-PROHIBITED PERSONS WHO ARE EXEMPT FROM REQUIREMENT TO HOLD A LICENCE UNDER PART 2
5] Any person who is of or over the age of 18 years who is receiving instruction in the use of a category A or category B firearm by or under the immediate supervision of the holder of a category A or category B longarm licence.
When carrying or using a longarm of the category specified in the supervisor's licence for the purposes of receiving the instruction at an approved shooting range.