You need AAA predictions at the lowest. A* comes from a 90% average across all A2 units, AS are irrelevant, you just need to have 80% across AS and A2 to make sure you have the A overall, including 90% at A2. For example, Maths you need a 90% average across C3 and C4, your elective(stats, decisions etc) doesn't matter. If you don't have AAA at the least expect straight rejections. If you get 90% average in a subject at AS your teachers will likely predict you an A* for A2.