I agree with the above.
In nature most territorial cichlids will guard a 4 ft square (@ 200 gallons give or take, depending on depth).
Any unwanted cichlid, be it an unreceptive female, another species (whatever) that traverses into that 4 ft square is dead meat, unless it can escape outside of its 4ft boundaries.
A 75gallon tank does not come close to a 4ft square.
This is why you might see a pair taking all but a small portion of a 6 ft tank as its own, and any other cichlids pressed into one small end, or hovering on the surface in a tiny, upper corner.
But you may say, a tank isn't nature, this instinct should not apply.
I believe the un-nature of a glass box, makes things even worse, because there really isn't anywhere for the one being chased to go.