think it all depends on the fish, I had a 2ft dovii living with a 9inch serverum for 3 weeks with no issues but when I tried a red devil the dovii got a bit angry! also have some full grown jags with rainbow cichlids, umbee, texas , red terror, green terrors and the tanks more peaceful then my grow out tank.
My advice if you really want the bigger cichlids dovii umbee etc it can be done its more a matter of how much money and fish your willing to risk in order to get that outcome its a lot of trail and error.