Aside from the fact you can instance BP with foliage since I think .19 or .20.
The way you are going about it and how you frames this question is just odd.
If you want an event to stop whatever it is based on distance, create an appropriately large shape and detect the End Overlap event to put a stop to whatever interaction was occurring.
You definitely will not find a way to get a reference based on location since location is always updating and even with an array map you have nothing that is constantly updating the data to keep track of the location. The overhead for that is probably almost as bad as not using instances (depending on number of actors your would have to trace to).
If you really cant use instanced blueprints, the best way would be to spawn a custom invisible mesh to use for the overlap detection. You just spawn it around the character, and use it to determine when/if the player exits the area via the same end overlap.