Contrary to popular belief, a lot of these large American cichlids do not form breeding pairs for life. When its not breeding time they do not live together or share & defend common territories. When its breeding time, any suitable partner will do although the selection criteria may be more important for some species. The female is usually more aggressive for festae in my experience.
So to answer your question, even a much larger tank is not big enough. Some people use other cichlid species to distract pairs and this over crowding reduces territorial disputes and/or single individual harrassment.
Since your "pair" are different sizes, you could get some egg crate or perspex and create a small holed divider which only the female can swim through. This will allow her to escape at will. On second thoughts, just use egg crate with no holes. They will spawn through the divider just as effectively. I once had Red Devils in 2 different tanks connected by a canister filter (and water bridge) . He would milt in the intake to fertilise the eggs she laid near the return. True story!!