Is this unusual behavior

On Tuesday, I added six yellowtail tetras (Alestopetersius caudalis) to my 60 gallon tank. The tank also contains six butterfly cichlids (a. thomasi) that have been in the tank for four weeks. I thought the tetras would occupy the upper third of the water column. However, they shoal in the lower third of the water column mingling with the cichlids. The tetras are wild caught. They are also feeding off the substrate and do not come up to the surface for flakes.

From the info I’ve found on the web this species typically inhabits the bottom-middle of the water column so perhaps what you are seeing is their usual behaviour.

Picture showing the entire tank?

They want more fish in their group, which is why they are hanging out with the cichlids.

If you have lots of floating plants or low light on the tank, it will encourage them into more open water. But most fish don't like being in brightly lit tanks especially if they are in small numbers.

It's a very open tank without much cover for tetras. There's lots of rocks for the cichlids but nothing for the tetras. Floating plants would help them feel more secure and more plants in general would help. Even if you put a pile of plants in one corner, the fish could hide in that if they felt scared.