How to use surface offset properly?

[Yorkst]

Here is a stream of particles with initial downward velocity and no gravity. The lowest object is a cube and the one in the middle is a box, though they both look like cubes in this projection:

Here I set offset surface parameter of cube's static object to 1:

 

It displaced the position, where particles appear after collision, by one. But didn't displace the position where particles start colliding by the same value.

 

I can achieve equal displacement by setting Volume Offset of popobject to 1. But it will affect collisions wtih all objects, not just the cube:

 

I also can use a bigger invisible cube in this particular case, but it won't do with more complex geometry. Can I achieve the result like in third picture, but only for a cube?