One thing i've heard of people complain about is Bob not using drafting/slipstreaming to make a pass. The same can be said for blocking/closing the door upon completing the pass. It amazes me that people have not discovered what i have.
Essentially, slipstreaming is the first step in overtaking & blocking is like the last step in securing your new position. Basically, both slipstreaming/drafting and blocking can both be achieved with the overtake command. By doing this, i've managed to train my bobs to make passes at the exact moments when i would.
Also, if you know your bob's faster, then don't keep telling him to increase. He'll only get too frustrated because he's being held up. I find that if you slow him down nearer to the pace of the other car just before he catches up, simply maintaining the pace that's only slightly faster than the other car's will see him inevitably pass anyway. He will stay out of the slipstream to avoid contact, but when you use the overtake command he will get in the slipstream until he's right behind his bumper.
Recently in a 24 HR Nurburgring race for example, he was able to slipstream and get alongside the closely matched rival. By repeatedly pressing the overtake command, he was able stay alongside him before finally making the pass. They were both beside each other for 3 corners, both leaving room for each other. That was very nice to see. And when he had gotten past him, i had to use the overtake command again to make sure he didn't let him back past. Until this point, he had been running 2nd and completing this move safely with a close-to-evenly-matched pp was very rewarding.
This way, you can pass much more easily and safely. I hope this helps.