Correct me if I'm wrong, but the raw internal marks sent by your school seem to be rounded, and the ranks are given off the rounded marks. I don't think rounded marks would be used to calculate your internal HSC marks, as that would be unfair to some students.
In your case, that would mean that your actual internal rank could vary from 11th to 15th. Note that your position within the cohort is used to calculate your internal mark (slightly different to using rank). As ranks 11 to 15 all have the same rounded mark, there would be little difference in your internal mark whether you are actually ranked 11th or 15th, as position-wise, your internal marks are very close to each other.
If all 5 students are tied exactly in their raw internal marks (same mark every assessment), then you would all get the exact same internal HSC mark, which would roughly correspond to the 13th best exam mark, although again, it depends heavily on how the cohort, as a whole, performs.
