In these pics you can see how sleek the ECOmmodore and Monaro are.
The ECOmmodore came in at a slippery 0.28 thanks to the steeply raked rear window which flows nicely onto the boot lid. This profile is shared with the Monaro.
The sharp lip integrated into the Monaro Bootlid is a big improvement over the VT/VX sedans rounded trailing edge. Unfortunately the Monaro boot lid is not a direct swap item with the sedans.
It does however give a hint as to what sort of improvement is required to the VT/VX sedans boot to help reduce aero drag.