Ok, maybe I'm not explaining myself clearly enough.
Let's take person A "Joe". Joe is (beyond all logic) a "truly average" person; he is literally the median in the state for every single subject available under the VCE if everybody in the state did every single subject.
Now, Joe is doing English, Specialist Mathematics and Chinese.
Without claiming to be 100% realistic, his study scores for the four are going to be approximately 30, 25 and 20.
Why?
English has a cohort which is pretty much the entirety of the state, since everybody must choose one of English/ESL, English Language and Literature. Furthermore, statistically speaking English has the largest number of people doing it each year, with about 100 people getting a 50 annually (and a few thousand getting in the top 8% of the state). From this, we can surmise that a VERY large number of people do English, including both the hard-working students and the students who are going to do nothing but get high on weekends. Logically then, Joe's study score for English would be pretty close to the median of the state, ie. 50.
Specialist Mathematics, on the other hand, has a much smaller cohort, with less than a thousand people each year getting 40+. Furthermore, the people who do it are typically within the higher echelon of mathematically-talented students, although at the same time there are "weaker" students who either just enjoy maths or want a high markup subject. The former (I am assuming) would typically be the majority of the people doing the subject, so as a result, on the bell curve, Joe is going to be in the lower half, since there are less people in the lower half of the state's mathematical talent pool doing the subject than the ones in the upper half.
Finally, Chinese is most likely going to be Joe's weakest subject study score-wise. This is because statistically speaking, by year 12, the vast majority of people doing Chinese already have some sort of Chinese speaking background (I can't say I have the article source on me, but if you look at the top scorers for Chinese each year, it should be pretty clear...). For Joe, who is a non-background speaker, this means he is going to be in the disadvantaged minority, as most of the people doing Chinese are going to be the ones in the "upper half" of the state who are above his "median" status. Thus, he is going to have a lower study score in Chinese than for English.
I'm not sure if I've phrased/explained some of that very well, but that's the general gist of it. I also realise that some of the premises are very silly (eg. the very existence of Joe), but the truth is that for some subjects (particularly Chinese), what I have stated isn't too far from reality...