Need help setting up lobby for endurance race

For anyone curious about the race itself, it will be part of a tournament we’re holding next Sunday. If you’re interested in joining don’t hesitate to check the details at http://forzatournament.tumblr.com/ and message Danny2010.

I’m trying to make sure I have the options set so that we can have 2 classes racing each other (GT and Prototype), each class is on the starting grid grouped by class, each class places only within its class, the race goes for 30 minutes (no lap limit), and it has an end race time of 5 minutes. The only thing I really need help on is the “Advanced Rules” tab when you are creating a private lobby. I believe this is how the Advanced Rules tab should look;

Scoring Type: Time Based
Bigger is Better: No
Compare Best Lap Scores: No
End Condition: Time
Race Length: 30 Minutes
Grid Ordering: PI
Ascending: No
Per-Car Roll Off Delay: 0 seconds
Number of Player Buckets: 2
Score Buckets Independently: Yes
Group By Bucket: Yes
Tag Enabled: No (N/A)
Number of Teams: None
End of Race Timer: 5 minutes

I leave the group 1 and 2 options alone (besides restricting what types of cars are allowed). I have actually tried testing these options out with two other friends in the lobby but for some reason when the two people who were in the same group passed each other, their positions in the race didn’t change. On the screen it still separated the two classes correctly but within the class itself, it wasn’t registering that there was a lead change. Also the race would end on time, but the end of race timer didn’t work. Was this an isolated incident and should I just try it with more people or am I setting up the lobby wrong?

Thanks ahead of time!