Be a bit careful when you say "93 goes to 92.8", because this can be misleading. The aligned marks (the ones you get to see) are not directly correlated to the scaled marks.
The purpose of the table is to show you what aligned and scaled mark corresponded to particular percentiles, not what aligned marks correspond to which scaled marks. Unfortunately, the format of the table makes it easy to come to that misconception.
RAW marks are modified in two different ways. One path is where they are "aligned" which gives the HSC marks and the other path is where they are "scaled" which contributes to the UAI. There are two different "algorithms" implemented, which are in no way related to each other other than the fact they start with raw marks. So trying to work out any pattern or equation between aligned marks and scaled marks is rather futile.
One single aligned mark can correspond to DIFFERENT raw marks, so it wouldn't be surprising if you see the same aligned mark have two different scaled marks, because the raw marks behind them may differ.