I know this is an old thread, but in case someone looks at this, I'll give my anecdote:
For me personally, I strongly disliked the way Further Mathematics worked out for me. I scored 100% on every SAC; my RAW SAC average was 100%, and I was ranked first. I scored 38/40 for exam 1, and 58/60 for exam 2. This means that in total, I lost 4 marks across both exams. This resulted in me getting a 46. 50(highest possible study score) - 4(number of mistakes on the exam) = 46. My friend scored a 45 and made 5 mistakes in total. Can you notice a pattern?
The reason its so difficult to score a 50 is because you virtually need to make no mistakes on either exam. If you're ranked first, you're looking at 1 study score down for every mistake you make. Further Mathematics is an insanely difficult subject to score well in, rather than the concepts, topics, etc, themselves being difficult. VCAA is also beginning to make the Further Mathematics exams more difficult, because it is becoming so easy for students to score well in this subject. This, in my opinion, is totally unfair to students who do Further Maths, who struggle with Mathematics. After all, it is meant to be the easiest of the three VCE Math subjects. But enough ranting, and I think I've gone off on a tangent, but yeah, that's my idea of why Further Maths is difficult to score well in; that is, above 45 in.