The 20" G2s for the 370Z are face 2, which has no lip. The 19" G2s are face 1, which has a lip. So if you want a lip, go with the 19's. It's that simple, folks.
Most of the pics of this wheel on 370Zs is of the 20's, so people don't realize that the 19's have a lip. Here's a pic of the 19":
Now check out this pic. The G37 in the foreground has the 19's, while the blue 370 in the background has the 20's. Those 19's on the G37 will also fit the 370.