I am interested too. I like jardinis and am curious about their aggression too. In my experience when they hit about 10 inches they just start savaging things.
Which is the experience of most Jardini keepers. But with 5 or 6 jardinis, who knows.
i've tryed that so many times, sometimes it works till they are about 25 to 30 cms, then they start killing each other... i've given up on jars together, but still i wish the best of luck.