Christ - getting sub-30 mpg figures in a 320i sounds pretty bad. My 325i auto gets 30mpg. Yes, its a lazier engine and doesn't need to be revved so hard to make progress, but its a 3.0 six so you'd expect it to be at least a bit worse.
Current: F30 318d Sport manual, AW, 18" alloys
Sold: R56 MINI Dooper 2010, Chilli, Bluetooth
Sold: E93 325i M-Sport auto 2007
Sold: E91 320d SE 2005
Sold: E46 318Ci Coupe 2002