After many 'runs' into the Den of the Fallen, I've finally come across a pack of Plague Bat Wallers in Patch 16!
It was always my intention to capture footage of these fascinating creatures at length in order to better understand how the affix works (other videos online have been disappointingly short :P).
Below are two videos - one demonstrating how a Champion Waller pack works and the other shows how Elite Wallers are different.
Champion Waller Behaviour: http://www.youtube.com/watch?v=B-59Qczm1hQ
Elite Wallers Behaviour: http://www.youtube.com/watch?v=D6yLHU7LirE
The screenshot below shows how it looks with a greater number of Elite Wallers.
EDIT: Would appreciate a mod rename the thread to: "Videos: Champion and Elite Waller differences" ^^