If your facility is accredited, that accrediting organization may have record content guidelines. Additionally, state licensure boards (in some states) spell out the appropriate documentation levels for providers (e.g., minimal requirements), but tend to be more vague than an accrediting agency. What I'm thinking of here is Joint Commission or one of the several others.
Especially for Radiology, the professional association (ACR) has documentation "standards". This sometimes holds true for other specialties, but I have rarely used any others.
Lastly, since the administrator is involved, recommend a revision or establishment of medical staff by-laws. They probably exist and give providers specific privileges and guidance on how to carry out their duties. For most organizations there is a medical record policy embedded in these and leveraging those documentation expectations appropriately will help the providers understand their expectations and hopefully improve documentation quality and detail.
This is perhaps the biggest challenge we face. It can be so difficult to select the appropriate code with a high level of comfort over that code selection when you have ambiguous or misleading health record entries. I hope some of what I've offered helps. Documentation Improvement is sort of the newest catch phrase for facilities trying to ramp up their record quality level. Unfortunately, it is sometimes the last thing some providers want to participate in...
Good luck.