OMG you are right Cat, what about change antiportals sheet by normals whit BSP brushes in it?
The author spend a lot of time optimizing collisions - may be he realized something at this point (optimization) -
On this subject I discovered a great tutorial but there's something that is isn't clear :
I quote
When EnableCollision is True for a material, all the triangles of the mesh that are textured with that material will be used for collision calculations. This means that the collision calculations will be based on exactly the triangles you see. This will sometimes be the same speed as but in most cases slower than using simplified collision models because there will be more triangles to calculate collision for.
Memory Concerns
Other than speed, there is a memory gain to be had by using collision models and not material collision. Even if the material collision is not being used, if EnableCollision is TRUE, collision data for the material is stored in the static mesh. With a large number of static meshes this can lead to a great deal of wasted memory. This Xbox memory optimization document talks about the memory savings associated with static mesh material collision. While the document focuses on Xbox, the memory savings are true for all platforms. In general, if you are using collision models for all types of collision (see Step 2 for more details),make sure you turn off material collision for all materials.
I saw that it isn't the case on Urbanstrike, the autor seem to use Kdop and collisons box without turning off the collision for the materials: is someone can help me to understand this point it should be great
In the same way while using Blocking volume, does it better to turn off collisions in the array menu of static meshes properties or in the materials?
This tutorial:
http://udn.epicgames.com/Two/StaticMesh ... rence.html
BTW I'm going to try antiportals first.
Edit:
Why there's is no Karma collisions? does it's the problem? :

- collisions.jpg (65.65 KiB) Viewed 8878 times
After refresh karmas collisions.

- karma collisions.jpg (59.63 KiB) Viewed 8878 times
does it need to be refresh?
a bit technical but I think necessary.
Edit2: i change my first sentence because there are effectively antiportals as green sheet.