Hi:)
I think this is what you were wondering so i'll clear up some confusion of doing more than 6 subjects over the few years. Let's pretend you are doing the following 3/4s in these years
2009 (yr11) Biology
2010 (yr12) English, Methods, Spesh, History, Legal
You decide to do an extra year undertaking Further and Chemistry. Since you need chemistry as a requirement, you are simply doing it just for that.
Let's say you got 40 in all your subjects in year 11 and 12, since you did six subjects, they take the top four including english and 10% of the other two.
And when you did Further and Chemistry, you got for example 45 in Further and 30 in Chemistry.
Further would then replace one of your top 4 subjects, and as a result one of your 10% subject would move into the 7th subject range and therefore not count.
Chemistry would also be outside the 6 subject and although it does not have any affect on your ENTER score at all, it serves as a requirement for the course you want to do.
Make sense?