I have two convicts that I believe are either dwarfs or runts, but they are only 3 to 3.5" and over 18 mos old. I rescued them in a community tank, and recently QTd them to a 20g.
They have never been in a good breeding situation before, so we will see what happens.
Anyhow the previous owner homed them with a variety of 7 African cichlids and 4 catfish, and they lived that way for well over a year. There was lots of chasing and some nipping, in both directions. Both tanks are more peaceful since the separation.