I've actually calculated this though. I was more than happy with the reading of 41 to 42 somtimes even 45 but I worked it out today after the refill and it is 34.1, and it's been pretty constant.
The miles since start since the service almost 1,000 miles ago is reading 37.5.
My fuel light comes on constantly at the 400 mile mark, usually between 385 and 410.