Not the answer to the question you asked but IEC 60601-1 provides a bit of guidance. They say that it is "difficult" to define the dimensions but indicates that 1.5 meters away from any point in the environment has been "justified in practice." (So if a patient is laying on a table, the patient environment includes the complete table; i.e., so 1.5 meters away from any point on the table). I can see a number of difficulties trying to exactly specify.
I am not questioning the 6 foot perimeter. We are questioning the requirements. An inspector on site is asking for test reports for the monitors we provided, but he is not asking for the test reports for the desktop computer or monitor that is sitting on the nurses desk right next to the monitor for our medical device. What is the difference? We need to get our hands on the AAMI standard he is referencing his information from.