agreed, no. What you could do however, is 4 neolamprologus lelupei, which is a small tanganyikan fish. They might work to fill the tank for you...
They are a beautiful yellow fish, with irredescent accents of blue and green lines. They could go in a 20, but you don't want to mix african cichlids with cichlids from south america (Angel fish are columbian, I believe), as there is a different tempermant, as well as water requirement.