Hi there welcome and thank you for the question hope i can be of some assistance to your problem
We at dealers get a lot of people complaining about the fact that there vehicles will not do the mpg that it says in the brochure now a lot of the problems can be put down to the fact the sales person will say that the vehicles will do exactly what the brochure says to the customer which is not the case, in the real world you will be looking at the vehicle doing around 10mpg less than what the brochure says and ford gave out sheets to the technicians to explain this to customers who complained and I will explain how this differance happens.
When the mpg figures are calculated it is done in a lab with the vehicle on a rolling road, now when a vehicle moves the tyres on the road are causing drag which will up fuel consumption but on the rolling road only the front wheels are been driven so they do not have any drag of the rear wheels so this will increase the fuel consumption figure.
The vehicle only has one occupant in it which is the driver and all the spare weight is removed from inside the vehicle spare tyres, fuel etc to bring the weight down in the car this again increase the fuel consumption figure.
All electrical equipment is switched of to take load of the engine and also the alternator is disconnected from the engine to remove even more load again less load on the engine will increase the fuel consumption figure to make it higher.
Now also this been done in a lab also takes out any outside factors like wind, road surface condition, stop starting at traffic lights / junctions etc, how much fuel you have in the tank speeding up and slowing down and so on, now there are many other factors that also affect why the figures do not match but I hope this goes a little way to explain why your figures will not meet the ones in the brochure.