NavMesh Agent determine if Destination is reachable

I need to find out if a NavMesh destination is reachable for an Agent. I can't use the pathStatus from CalculatePath, because whilst that returns PathPartial for locations which clearly cannot be reached, it's also returning PathPartial for locations which are clearly reachable to the Player's eyes, but because for some reason a tiny percentage of the path cannot be reached it's got the same status as the former. I need a more nuanced approach, to determine if the path is say more than 90% uncompletable. Are there any suggestions on how to achieve this?