there is a map in the ecu that controls the ratio of port to direct injection. it's completely configurable, and oddly enough the factory map uses the di heavily at higher rpm (up to the 5200rpm scale of the table), which i'd imagine to be backwards. for my turbo setup i had to increase the higher rpm range port ratio to keep up with the fuel required.
here's a pic of the stock (hot) map:
in total there are three maps (cold, warm and hot) and another to control the temp thresholds at which they switch.