Pflow: Particle following a spline, but they should come closer together after time

[Badsmile]

Hi everyone,

its been a very long time since I worked with pflow. So maybe the answer is very easy, still I cant figure it out:

I have particles following a spline through the "speed by Icon-trick". Now I want to achieve an effekt where the particles have more variance to the path follow at the beginning and as time goes by, they should stick closer to the actual spline - basically a tapered particle-Stream. I made a little ugly painting to explain it better.

How can I achieve this? Thanks!

[Diffus3d]

Maybe you can link a gravity to the speed by icon helper and let the particles slowly be attracted to it.  They'll start out wide and then get thinning, though they might get a bit erratic without some drag or something.