Simulation distance not working as expected

We are on a Purpur server and recently upped our simulation distance to 8. From everything I have read online I am led to believe that having an 8 sim distance means the player stands in chunk 0 and then loads an additional 8 chunks in each direction. However, while running a world eater the dupers in the 8th chunk continued to fly as intended but did not dupe TNT. Am I misunderstanding something very basic?