It’s probably more than just particles. something in that cloud has to be large enough to actually reflect the intended radar wave length.
Usually that's the X-band, so that's about 3.75 to 2.5 cm, but you also need to consider seekers using the Ku or Ka band.
The chaff decoys are set like a menu. The ESM picks up the threat missile's seeker's wave length, and then the computer picks from a palette which decoy to use to match that wavelength. That's why the DLS is part of a set:
Type 726 EW set.
Type 726-1 ESM, Type 726-2 ESM, Type 726-3 ECM, Type 726-4 DLS.
One ESM is for signal analysis, the other ESM is for directional finding.