Quelea Polysurface Environment Problem

Hello Everyone,

I have been using quelea for the past month, so I am still familiarizing.
I have created a polysurface in rhino which represents my roof.
I am trying to use particles to simulate visually how rain would spread across the roof.
The issue is that when I let the particle run in a free environment it's fine (left image). But when I assign the polysurface the particles are attracted to a specific edge.
Any idea what's happening?

Thanks in advance!

Alexandra