E/M vs. 90792

The CPT® book states that some psychiatry services may be report with E/M's or other services when performed. E/M services may be reported for treatment of psychiatric conditions, rather than using Psychiatry Services codes, when appropriate. Can anyone give any insight to what 'when appropriate' means or how to apply it? I have providers that use E/M for any service other than individual or group counseling. I don't think that Diagnostic Assessments should be billed as E/M but the providers disagree. Any input or resources is greatly appreciated.