You would need to set up different clients (APs) in the NPS, so you can easily differentiate between them in the NPS.  Lets say you call the clients SITE1-WIFI and SITE2-WIFI with the IP ranges of the respective AP's.  Then in the NPS you can set up policies and use "Client Friendly Name" with a value of "SITE1*" - this will affect only requests coming from APs that are in SITE1 and so on.  I hopefully understood your question correctly 😉 
						
					
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