Hey Tyler..... in my case (as I'm sure not all cases are the same), I have been successful at putting much smaller bichirs with larger because:
-- I have a large group (bichirs do well in LARGE numbers)
-- I have had extremely agressive bichirs in the past....... when you have one of these, it will be obvious...... take it out & sell it...... or simply get rid of it.....
-- Keep them nice & full
-- Use garnet substrate..... PERSONALLY I think garnet (semi-precious stone) has a calming affect on bichirs.
-- Throw in a piece of driftwoof if you can..... again this makes bichirs happier......
-- Use LOW or HIGH lights...... bichirs WILL get used to brighter lights..... just takes time.
-- Bichirs tend not to cannibalize
-- You will have more problems in a baby grow-out tank where they are in their "nipping" phase.