I don't have images to proof the charm triggering, but I've seen a brazilian streamer showing it live.
The charm triggers and it's effect happens in the same SQM of the creature that died. It works like a plus (+), it doesn't count in the diagonal, because that counts as more than 1 SQM.
Here is an example:
The targeted Gazer after dying will explode and damage all adjacent Gazers. That means it can only hit 4 Gazers in total if he was at the same SQM that I'm in (closed box).