HowTo: Audio Ambience in Arbitrarily Complex Area

Question

I'm trying to solve the problem of creating a reliable ambience across several arbitrarily-shaped regions of a UE4 map.
These areas aren't generally bounded by splines since they might have holes in them or severe concavities (I've read the post about spline-based volumes).

The  Wwise solution that seems to fit is scattering a collection of positions into the world and using AkComponent's SetMultiplePositions() call to enable them for a certain sound source.

Is this a performant approach? Also, there seems to be a limit to the number of positions that can be set (around 1100) and would like to know why.

Finally, Is there a better solution within Wwise I'm overlooking for a large exterior open-world space of this sort? Thanks.