Hello,
I'm far from experienced on the topic (I've decided to try and involve myself a bit more....)
I recently caught 2 of them about 6 or 7 cm and about a week ago I caught an 8 cm one and the other two were picking on it (In a four foot tank, seems unnecisary to be territorial when so small.....)
I added some extra caves and a couple of Inanga, the kokopu is still a bit timid but he doesn't let the other two chase him now.
Also both my inanga go really creamy and lose their patterns when they get stressed.
Hope I helped.