Why does the Audi A1 have four-cylinder engines instead of six-cylinder like other Audi models?

I am considering purchasing an Audi A1 but I am confused as to why it has four-cylinder engines when other Audi models have six-cylinders. Can someone explain the reasoning behind this design choice?

The Audi A1 is designed to be a smaller, more compact car and four-cylinder engines are more efficient for this type of vehicle. It allows for better fuel economy and less weight, which means better handling and performance.