Here's my biggest rig, a Zob with zobello perc...about at the minimum with water level. 18mm female joint. 700 on the NV controller. About four terp balls spinning in there, and after some experimentation I can say that they do help with the airflow. I don't know if they help by creating a whirlwind or something, but definitely helps me with the chugging on a bigger airy rig when capped.