it maybe risky adding small rays. the aro is pretty big. size difference is an important factor IMO. Another important factor would be how social your particular arowana is. If its a good community fish and you have added smaller fish in the past then it should be ok. getting bigger rays would be your best option. good luck.
Hello,
I use to have a 22" Gold Panda which was a bit naughty with the rays especially the flower ray however I have a 18" Banjar whuch is fine with all my rays..
I think it depends on the Arowana in question.
Just from my experience..
Thanks
Lee