I'd say thats about right, I know when I did the maths on the G40 Rally weekend up in the Peak District, on the 2 tanks of fuel I used on the run up, around the Peaks and the run back down to South Wales, I calculated 40+mpg. I had the missus and my son in the car(so was driving conservatively), plus a boot full of stuff too!
Mines modded(around the 150bhp mark) I still average about 34mpg on the daily work run which is 23mile on a mixed bag of roads mainly dual and motorway, which in my opinion is brill.
Though if I want to play daily I can soon drag that figure into the mid 20'sMPG(average), and with some key drafting of suitible trucks 40+MPG is never far away.
If you've got a poor economy then its probably down to a fault somewhere, or the ECU map is not suited to the mods that you've carried out(or you got +200BHP in which case
who cares!!)