what other types of rays can i keep with my 7" retics

[Conner]

I was under the impression that anything smaller than a Ceja or China ray could get along well together...

When you consider that retic's will likely only get half (or less) of the diameter of an adult motoro (or leo, hen, etc), as well as being much less aggressive naturally and during feeding, there is a real possibility of the smaller rays being picked on. While they may get along perfectly fine, there is still the potential for problems, and any ray keeper should be ready and prepared to separate rays due to aggression issues.