I think it was Stefano, but it might have been Aris, I can't remember... Well, he said that to get the best out of the AI you should let them run practice or qualifying laps so they can sort out who is going to be the faster drivers of the upcoming race. Otherwise, you end up with some of the slower drivers starting in the front of the pack and the quicker AI drivers are "blocked" by them - especially on those first couple of laps.
I know that I didn't exactly quote what was mentioned regarding this topic, but I'm sure you can find it on the official forums if you look. I can't wait to try v1.7.. Personally, I have good races against the AI 95% of the time. I just hate when they freakin' pit maneuver me!!