Mesh doesn't detect all collisions

Hello,
I have a mesh like this : http://i.imgur.com/B7Pfbot.png (made with a plane), its physics is sensors and it has a collision sensor (with ‘Triangle Mesh’ as Collision Bounds).
The problem is that the mesh detects only the objects who fall on the red zone and I can’t understand why.
Any ideas ?

Thanks.

You can enable Show Physics Visualization to see what the Physics engine sees.

Sensor objects only detect intersections with their faces according to the bounding type (in your case triangle mesh). This means if you have a cube inside a cube -> no intersection = no collision.

I don’t understand well since it’s not really a cube inside a cube.
Here is a screen with the Physic Engine : http://imgur.com/qeTKvNn (Notice that in that position the four (static) cubes will be detected by the mesh but if I move it on the right or on the left, some of them won’t be detected anymore).
I’ve even tried to replace the whole mesh by a single plane and I got the same problem.

To clarify, sensor objects “can” calculate depth or rather volume collision. But you have to use the other collision bound types say box for instance. Triangle mesh collision can only calculate the surface as stated.

Oh ok, thanks for the clarification. I changed the collision bound type for box and move my mesh to have only the bottom as a collision surface.
It will do it for now.