The pattern_distance is the distance between two neighbouring circles (be aware to be consistent with units of length throughout your application). You could also try to calibrate without ROS first to see if it works. You can just link to it as a library.
You could leave pattern_neighbor_distance to 0, this is just optional to average noise around the detected circle point. (I should indeed clear this up in the documentation and in the code, now that I look at it, it is quite confusing).