Leave the car in normal and it should get better. Comparing the CT to the C220 CDI is daft. You don't know what kind of driving is going on in that car. If it's sitting near a motorway it'll be getting 50mpg easy. It's just as daft as comparing your mpg to other members mpg. For example, my wife gets 30mpg in the IS. Other members get 45-50+ mpg. It's all down to personal driving style, acceleration, braking and trip duration as well as engine temperature, fuel quality etc etc etc. Too many variables to take ino account but my gut feeling tells me that 53.2mpg is impossible in a C220 CDI unless it's sitting at a constant 60-70mph 90% of the time
I know because I had one! It goes to 27-33mpg when driving in town.
With your driving if you got a diesel youd be worrying about DPF issues down the line. DPF got clogged twice on my C220 CDI along with other issues.
Also considering the C220 CDI sounds like a tractor, it's not exactly a luxurious experience, it's a rep mobile built only for high mileages