It depends very much on the width of the wheels.
This one shows something like the stock wheel and offset, it might even be more, with the same size wheel but with a lower offset to move the wheel out more flush with the arch.
The second pic shows the same movement out of the wheel lip, but with a wider wheel, the offset has had to redude less, because there is more wheel either side of the center line.
It might help to do some comparisons on
www.willtheyfit.com with wheels you know, eg the stockers and maybe those big alloys you had on it to get an idea of what dimensions to change.
When comparing wheels of the same width te higher the offset the flatter faced the wheel will be (the wheel will be moved further in to the wheel arch), the lower the dishier it will be (the wheel will be moved out of the wheel arch), but like i said it all depends on width because offset is calculated from the centerline of that specific wheel.
Hope thats of some sort of help. You are pretty close, so if you want to try some of my wheels on it you could have a run down the A3(M) one afternoon.