The running plate from the cab curve was higher on GN than the A1s - it came up higher over the driving wheels, negating the need for splashers. This was something which I had to attend to in my own build some years back. Therefore, the curve is not deep enough on your running plate because the running plate above the driving wheels isn't high enough.
My apologies for throwing in a possible spanner into the works.
![Embarassed :oops:](./images/smilies/icon_redface.gif)