Quelea Flow down surface force Grasshopper

Hi!
I have been working the script to resolve the Flow Down Surface Force, which would help me to analyse the water performance on the surface.

I have been using the Quelea plugin to apply the agent-based system in grasshopper. However, I found that I am stuck at a certain point.

The points don’t flow on the surface if it makes sense.
200614_Kat_Surface_water_particle.3dm (45.5 KB)
200614_Kat_Surface_water_particle.gh (12.9 KB)
I would be grateful for any help.

Kasia