They've grown well. It's interesting that they haven't started causing havoc yet. Perhaps you've gotten lucky but there's still time. The sheer bulk and attitude of this species should not be underestimated. My old pair had to be moved from my 6x2x2 after putting on some serious size (14" female and approaching 17" male). From my experience it's similarly sized fish that bare the brunt of the aggression. It wasn't until mine passed the 12" mark that they began to cause too much damage up until then is was the usual bickering and squaring off. They were moved into a 10x3x3 and after a few months there they again had to be moved. I know the guy who took them had a 8mx8m tropical pond. I saw a short video of them in there but that's the last I saw.
Surprisingly there hasn’t been much aggression yet. Some chasing but that’s it. Doubt I’ll get lucky in the long run though. Still have a bit of growing to do.