That's harsh (the 'rubbish' comment). I've done just over 13k miles, the ECU mod and 5th injector have been done, and I'm getting an average of 40.6 mpg. The car did appear to improve at 10k miles as had been predicted. Perhaps your 5th injector is clogged? When mine was I was only getting 33 mpg at best.
Just my tuppence worth :)