Particle collision

Using UE 5.4

I’ve got a particle grid that I would like to react to geometry once the geo is being moved through the particles. A bit like a ship displacing water.

I’ve tried moving a sphere through the grid to no effect. However my collision works fine with my floor once I activate gravity (first part of the video).

I deactivated gravity so I am left with my particle grid wall which is the shape it needs to be when interacting with geometry. After that I duplicated my floor, scaled it down and am moving it through my particles, but nothing happens. (second part of the video)

What am I missing / do I need to do to get this to work?

Any help or pointers would be greatly appreciated.