I was under the impression that the Paratilpia Polleni get around 14-16", very thick, and very belligerent towards tankmates..
I also have a belief that many of the tilapia cichlids and west african fish have very unpredictable dispositions.. Kribensis and Jewel Cichlids at times can live with certain tankmates, and destroy other tankmates..
I have also heard a theory with Tilapia Buttikoferi that they are very mild-mannered up until about 6-7", even to the point where they will get picked on by other cichlids and I myself have had african cichlids kill juvenile Buttikoferi.. But, when they hit that 6-7" range, a ticking timebomb goes off in their head and they become very dominant and kill all tankmates..
I have seen it happen before... My current Polleni is about 6" and does not hold his own well with other big cichlids.. only tries to kill the other Polleni.. They have very interesting combat methods compared to Africans and SA/CA cichlids.. They don't flare and lock jaws like i've noticed with other fish, they just get nasty and bite faces and eyes in quick dart and move attacks.
my 16" Buttikoferi kills everything.. but lost a handful of juvies to a group of Mbuna africans in the matter of a few days..
Very interesting fish.. just my observations.