Your internals do not scale. UAC and BOS do not scale your internal marks.
Your school may choose to scale your internal marks to fill up relative gaps so that certain students do not stuff up others but no.
Your school sends your internal mark and rank to BOS. The performance of each cohort in your subjects in the HSC exam, determines how your internal marks are moderated. For example if everyone does shit internally in your school, but does extraordinary well in the HSC, that gives BOS an indication that your internal assessments were difficult in comparison to the HSC and your internal marks would be moderated to a higher mark. This could also happen the other way. After the internal marks have been moderated, you receive the mark based on your rank. If you're 40th, you'll receive the 40th highest internal mark. Whatever mark you get in the external exam, you keep that.