1. Does the BSP system cull entities that are behind visible geometry? Ive read around the forums, and the only thing I see is that BSP only culls geometry and havent seen entities mentioned. I know entities are culled/disappeared when they are out of the camera range (viewing frustrum?). Ive looked plenty around the web but I couldnt find anything about culling entities, and even if I did find something I wouldnt know how the entity culling would work in A6(if there is any). If I placed 700 wheat sprites behind a large wall, are those sprites being drawn?

2. I know the backfaces of entities are not drawn, but what about the faces that are not facing the camera? A backface such as the inside of the back of a model's head is not drawn, but what about the outside of the back of the head? (did I get this backface defintion right?) The reason I am asking this is because I copied a perfectly flat terrain about 9 times and I got a max fps of 40 when all were in view. However, I go into MED and make some large hills and go and run the 9 terrains in WED. I got a max fps of 60 when all where in view. Im guessing the jump in FPS was due from the engine not drawing the faces that were not facing the camera.

1) basically the bSP tree works in this way: it calculates potentially visible areas... so if an area is not potentially visible from where you are.. everything in that area is culled, including entities (except sometimes transparent entites).

2) backfaces are always culled unless you turn it off in a material. This measn any face not "facing" the camera is culled.. the math is pretty simple but i dont know offhand what amount of degrees it needs to be to be not facing..
anyway, this includes the faces on the back of a head model or whatever.. it applies to any face. Your analysis of the terrains and fps thing is correct.

!!!

1.) Im sorry I didnt try out my test level thoroughly, but I was using entities that where alpha dependent on camera distance. Thats probobly why I was reading alot of entities behind a wall, which is why I asked this question in the first place. When I did try non-transparent entities, you were exactly right! The visible entities count dropped when I was behind the wall.

However I did notice something... While I was behind the wall, and the entities were being culled, I noticed that the SRV was 2.0. But when I moved into view of the models (they were unnassigned flapping birds), the SRV went down to 1.0. So from this information is it safe to say that for this isolated incident that the engine used more CPU in hiding the entities rather than showing them? I know there MANY more factors in factorizing this, but is that a general conclusion for this scenario?

Well, its good to know that entities will be culled. Because of this I hope to start a little tutorial on culling in large open areas...

2.) So its generally safe to say that a hilly and mountainous terrain is much more efficient than a reletivly flat terrain.