I think something else to consider is the difference in systems......
For me feeding a tank full of preds and feeding a tank full of preds that live over rays you're trying to reproduce has been a little different, mainly way more food....... Every tank has rays. So you have to just keep dropping food in till the fish quit eating or at least let enough down to the bottom for the rays to get full. I think a lot of predatory fish tolerate each other much better in these particular circumstances.
I'm sure the ray filtration, tank size, and water change schedule might help too.