I don't know too much about Syndontis but they do appear to get on the larger side. And catfish are very good at eating anything they can get their mouth on. I know that the cory catfish and the RTBS can get along as my brother has kept both together for over a year with no problems. He also kept the RTBS with some yoyo loaches and had no problems (then a freak CO2 accident killed the RTBS).