Incident to rules ~ insurance's other than Medicare ~ switching it up

Question~can you bill a PA under their own number to Medicare and then bill under the MD number for all other insurances?
And if you can what are the rules for the MD not being in the office suite, can they still see patients as long as the MD is readily available? And what defines available?
Or si this differnt for each payor?

Thank you sooo much in advance!

incident to

you bill the provider that rendered the service to the patient. Under "Incident To" (a Medicare provision), the physician had to perform the initial service and subsequent visits (for same condition), can be billed by NPP (per state License). Private insurers may or may not cover NPP services. You need to check with the commercials to determine their policy. If the commercial tells you to bill under physician, have it in writing.
For Medicare, under Incident-To, the physician must be in the office suite and immediately available to assist if needed. Available has been defined as within shouting distance in suite, not another building.