Jar with Fireflies in Blender [HOW TO?]

[AlphaChannel (Dr Salty Lout)]

Particles collision problem

I am making a simulation with boids particles inside a mesh (I have applied collision physics to the mesh, inverted the normals and applied all transformations) and for some reason, the particles do not collide to the edge of the mesh and leave a gap from all sides. How can I fix this? [enter image description here]

see this post.