A couple observations on the topic of centerpiece fish.
The first one is how one defines centerpiece fish. If one has in mind a largish fish with a number of smaller fish, the tank has to be very large for this to work. It is not really "natural" to begin with, because you will very rarely see this in the habitat of most fish. As responsibnle aquarists we need to keep in mind the natural expectations and needs of the fish we intend keeping, rather than some arbitrary "artistic" aquarium--in other words, what the fish need, not what we want.
I don't know if there is a term for this, but my idea of centerpiece would be say a 4-foot (120 cm) long tank with a shoal of Congo Tetras (12), or a group of six or seven Pearl Gourami, or a group (12) of Bleedingheart Tetras. Around whichever one of these one chooses, there could be largish groups of smaller species such as one of the Trigonostigma rasboras, or hatchetfish for the surface, or a group of 20 Corydoras for the substrate, or a group of 5-6 of one of the smaller loach species, or groups of the "Rosy" clade tetras, etc.
Another method for a centerpiece would be a group of discus or angelfish in at least a 4-foot (120 cm) long tank, with carefully chosen tankmates (very carefully chosen, given the requirements and/or temperaments of discus and angelfish).
Working with smaller tanks poses some restraints, and frankly makes centerpiece fish almost impossible. In a 29g at 30 inches (75 cm) length, no fish over three inches (7-8 cm) is suitable (with a very few exceptions). A pair of dwarf cichlids with suitable dither fish is an option, or a pair/trio of a peaceful gourami with suitable dither fish would work.