I'm not sure how 4 body lengths make it an appropriate home. I can't imagine it would be very active, or interesting to watch for that matter, in such a small tank. I honestly don't know what kind of enjoyment one would get from doing so. But that's me. We all have to decide for ourselves how much space our fish need to swim.
125 - BGK, chanchito cichlid, pictus cats, silver dollars, palmas bichir
125 - cichlids (severums, bolivian rams, chocolate), rainbows ( turquoise, red), loaches (angelicus, zebra, kuhli and horseface), plecos (BN, RL and clown), denison barbs, tiretrack eel, pearl gouramis, betta
90 - Congo tetras, african knife, upside down cats, spotted ctenopoma, kribensis, delhezzi bichir
2.5 - betta