@MieszkoZ Sorry to disturb but do you have any idea ?
For the moment I make a circle with 3 locations around each wall so I am sure one return true on “does path exist”. Then I go through all my buildings and find the closest one so I can actually have the actor instead of a location next to it. But this might get very pricey when running on a lot of AIs.
I do really feel like there is a simple variable for the outside navmesh search radius or error margin I could tweek a bit to solve my problem easily 
Cheers