I've found Zebrina get more aggressive as they get older. My pair is very aggressive and will chase Rays, bass, and make life hell for its mates.
Keep in mind, I used to keep my pair with discus for over a year. Until they started chewing them up.
My Tapajos are much less interested in their tank mates. That being said, they don't back down when messed with.
My take...Tapajos are more tolerant of tanknates than zebrina.