Check your driving style by re-setting the fuel trip at different speeds etc.
My dCi will do 99mpg at 40mph in 5th, but only 36mpg at 100!!
Also think about Advanced Driving - its dead cheap cos tutors are trained volunteers (about £50 with the Institute of Advanced Motorists, IAM), youll get better economy by anticipating better, hardly ever need to stop at roundabouts by good timing and youll learn about road positioning for better faster lines and sustained gear changes (throttle open). Its not just for nerds with Volvos.
PM me about IAM, I used to be a Tutor!