
theheadkase RPG Superstar Season 9 Top 32 |

If you look at the section titled Determining the Outcome on page 320, it says each round you make a gunnery check to see if you meet or exceed the target's TL, if it is ever less then the projectile is destroyed.
While it doesn't have an official ruling for hiding behind an asteroid I would assume you get some sort of cover bonus to TL as the target.