I have observed that, my fish will not tolerate others in their space at all unless they are attempting to pair up. When it is getting to be that time when the female is almost ready, my male will quickly chase her everywhere around the tank. The other side of chasing is territorial, and mine usually end the chase quickly at their boundaries, or just spar with each other. A dead sure way to tell that they are a pair(not nessicarily m &f) is if they are picking/cleaning a rock or making a pit to lay eggs.