I have a TSN and an RTC in with my rays at the moment, but everyone is close to the same size. No real problems as of yet, however, things do a get a bit hectic when they all go for food at the same time.
I think my female motoro is in love with my TSN, she likes to lay on top of him and he lays on her. My little RTC will shimmy under the rays during feeding some times and try to get food from underneath them.
They all seem happy for now, but the cats should be in a much larger pond by summer. I've heard a lot of rumors of rtc's eating rays like burritos, but I have never heard of anything first hand.
The video link in my signature will give you an idea of how they all behave.