Problems with Tying Particle Emission To Vertex Weight Proximity Group

My eventual goal is for an explosion to sweep through a ship, with sections of the ship emitting debris as the shockwave reaches them. To do that, I’m trying to link particle emission to a vertex group, and have that vertex group use a vertex weight proximity modifier, so that as a target object indicating the shockwave moves, different sections of the mesh release particles.

The problem is, right now in my mock-up, the particles are being released uniformly despite my vertex group being assigned to the “Density” area. What’s the problem here, and if this is a bug, is there another way to achieve what I want?

My scene is here: StaggeredExploTest.blend (1.4 MB)

P.S. Is there any reason why baking my particle system causes it to show up as a hair system?