You don't need to have the CPL on the drone when figuring out the setting... just look through the filter directly when you pointing it in the same direction as you later will take the shoot, there adjust it until you have the strength you desire.
When I use a CPL on my camera outside I typically frame my shot and then rotate the CPL while I am looking through the finder until I get my desired result. Simple. I just bought a Freewell CPL for my Air 3. I tested it today and it works fine...
Normally my business is focused on construction but this was for a real-estate gig but not shots of a house - it was for a realtor to produce a promo for the city for folks looking to move there. 11 locations to shot - 1 minute clips for each...