Bear in mind PTPTN full loan in public Uni and private Uni offers different amount.

And like what fruitie has said, they look into your parents salary, as well with some other critirea. One of it is amount of people in that family.

okay.
Just give you some cases or scenario.
B parents is 3.5k per month. B is the only child in the family. He applied for PTPTN.
He get approved, but then probability he get a full loan is very minimal since he is the only child. He will get either half-loan or the minimum loan available.

C parents is 3.5k per month. B have another 5 sibling. Bla Bla Bla.. Loan approved. Probability he will get full loan are much brighter than B, and it also depends whether the other sibling are working or still studying.

As I said earlier, this thing is hard to decide. It is all under PTPTN bureaucracy. If you are not satisfied, you can always appeal. They will look into it.