The airflow within the Bullet works a little differently than most other roasters. There are two inlets, one each at the front and back of the roaster. Cool air entering the roaster from the front inlet is pulled through and heated by the drum itself. Cool air entering the roaster from the rear inlet then mixes with this warmer air as it streams into the drum, before being pulled out through the exhaust.
This means that the air entering the drum is partially heated, and higher fan settings will cool the roast. It is for this reason that many Bullet R1 users keep their fan speeds below F5 for the entire duration of the roast.
That said, you can also play around with higher fan settings at the end of a roast, just be sure to adjust the power settings higher to compensate.
See below for a visual representation of the airflow within the Bullet.