EDIT* Yes it is trying to render everything it sees that isn't blocked, clipped or back-facing.

(From my little knowledge) When looking at a wall you are not rendering much. I know anytime you look dead into a wall up close you frame rate will be highest if the rendered scene is basically empty . The more the camera see the lower the frame rate. Using LOD and shared texture will help reduce this. And setting a short clip_far range and fog help. As for shaders I know nothing really but the post I have read from the real experts here point to good shaders moving processes to the GPU and increasing the frame rate. Make sure your LOD's are good steps. For far away objects stop their animation and kill everything you can attached to them. You can restart it when it comes close again. Dropping only 10% of the polys each step of the LOD may not give much advantage. Flat texturing your level will increase Fps but Y would you? Anytime you move from seeing little to see much there should be a drop but it should be reasonable. Light setting and shadow setting effect a lot too. The more info you give the forum the more they can help.

<- I Tried but a real expert will most likely reply to you soon.