Midland - if you are hearing both on a regular basis (and i believe you!), in this case i would take the chance of professional one-upmanship, and use the phrase in the reply 'remain outside CAS' ! 2 sheds point is quite valid that either KCOCAS or RCOCAS could be misleading - especially if a foerign pilot is involved. The word 'clear' should not be used in this phrase at all.