Near Camera Fade (particles) not working for me

This “near camera fade” setup doesn’t seem to have any effect when inside an arbitrary particle system (e.g. P_Black_body).

When I add it to a particle’s material, compile, run and go inside a smoke particle system, the particle sprites passing through the camera can still be seen fluttering/flickering noticeable.

Note: the SphereMask is doing something because I can adjust the radius (distance) at which the particles disappear, but the hardness doesn’t change how softly the particles fade out.
Hardness settings of 1, 10, 100, even 500 just does the same abrupt/hard sprite disappearance.

Can someone confirm whether it works for them?