My son was based in Mosul. He reported the same tactic. A timer on the rocket; set it and leave. Most detonated against the fence or fell outside the fence. Occasionally one would fall in the compound, once during morning muster. It detonated against the wall of the building in front of everybody. To their surprise not a scratch on anybody.

It erodes your mental health, never knowing when a random explosion might happen. Damaging in its way just like a bullet.