city driving is defined by a certain number of stops, driving with some certain speed and, what most important - with hot engine.
your mileage might be affected by terrain where you drive (hills?), your style (the style you used driving 325i does not have to be a good one for Soul - does Soul have 2.5 L engine?), weight you carry in the car, and, what is very important - mileage/age of the car.
I noticed improvement in my Rondo after 5000 miles, and it was getting better up to 10k miles.
Another thing was driving - it required different style of driving comparing to Intrepid (both have the same size on engine, but transmission allows me to save more in Rondo than in Intrepid - engine braking).
So, first get a ScanGauge II (helpful tool to show you how you drive, how much gas you use). Wait till you reach around 2000-4000 miles. The engine requires brake-in period. And it takes longer than 600 miles...
In city driving I got top 25 MPG (US) in Rondo, but with heavy foot - drops to 15-18... but at least I have fun

Hot - cold: the same trip, the same day. On cold start I got on average 16-18 MPG, while start on hot it jumped to 21-23.
I did squeeze more than sticker says, but it costs me (in terms of being patient and consistent).