I still don't get how people estimate UAIs by ranks. Do people just guess? Ranks can have significant differences in different schools. You're most likely to get the same external marks then your internals unless you do subjects which align really well.
I've been told that business studies doesn't scale well but the rest of your subjects are okay, especially adv. eng and economics. adv english actually scales about the same as ext. I and ext II english - not sure why though...
economics scales better than physics and 2 U maths scales alright... not sure about geography..
but really its all relative, all subjects actually scale down except ext I and ext II maths, the difference is just by how much - the less you get the more it will scale down so its always better to chose subjects you're good at...