Depends what sort of driving you do.

If you're doing nothing but long open-road journeys of 50+ miles at a time, you should probably get more than 48mpg. If you do a mix of short hops and the odd longer trip then 48mpg is good.

A smaller engine doesn't always give better mpg - especially in modern cars, which are very heavy compared with their equivalents 10 years ago. Your Mazda is at least 1.3 metric tonnes which is a lot of metal to lug around, and that's typical of cars in the same class.

It's a sweeping generalisation, but smaller engines generally produce less power and torque, and usually over a narrower rev range, than larger-capacity engines. The larger engine doesn't have to be worked as hard to move the car along at typical road speeds, which means it can be as economical as the smaller engine when doing the same type/mix of driving.

For what it's worth, I'd say 48mpg is pretty good for your driving mix, to get more than 50mpg regularly from a medium-sized hatch is rare.

We had a Focus with the same 1.6 TDCi engine. In similar use it would do the high 40's thus your 48 mpg looks spot on to me. On a longer run you could get as high as 57 or 58 mpg. The problem we found was the warm up time, it took the longest time we have ever known, at least 6 miles in summer, 10 miles or more in winter which really hurts the MPG.

It will get better as the miles pile up, our current Kia Ceed has 30,000 on the clock and continues to improve.