How "chance" works with bomber component?

How exactly does the "chance" parameter work with the bomber component?
I'd assumed if you mapped it with, say, a black to white linear gradient, that the majority of particles would land on the white side, tapering off in the gray (middle) area and not occurring at all where it's 100% black.

Yet when I tried to set it to only put ONE particle in a limited space (that is, a mostly black matte with a small white patch) the particle doesn't always appear. Instead of of putting the particle within the patch, it seems that said particle is placed randomly within the field. If it lands near the white patch, it's visible. If not, we don't see it. Is this how it works? If so, is there a workaround to let a particle always appear within a limited range?

I may have perhaps an example of bomber particle distribution that maybe could also help

Xia Script By xirja

This filter uses Tiles with different grayscale to modify the chances of bomber