I have a 5” Salvini in a 180 gallon tank with 4 Severums, an Oscar, a blood parrot, a firemouth and 7 geophagus tapajos and he hangs out with my yellow severum. I guess they like similar colored fish because they are pretty inseparable. They have their corner under some driftwood and will flare up at all the other fish but the Oscar.
For me my most aggressive fish in this tank was my electric blue acara which I had rehomed. Never heard of an aggressive EBA but this one would fight everyone including the Oscar who was 4x his size at the time. He never hurt the other fish but I was worried he would hurt himself.
You just never know with fish sometimes