Simply put:
A: Ranked 2
B: Ranked 1
Externals
A: 99 (highest mark)
B: 95 (2nd highest mark)
FINAL
A: (99+95) /2
B: (95+99) / 2
B will always get the highest external mark as their moderated internal mark and they always keep their own external mark. So if they mess up their externals, say 70, (70+99)/2, hes obviously not going to end up with a final HSC Mark higher than you.
Leading to the same mark. In reality, then 2nd ranked person does not simply get the 2nd highest external mark as their moderated internal mark, that will depend on the difference in marks between 2nd and 1st in internal assessments. Thats the essence of it.