Weird FPS drops when staring at wall. PC

[rumisterx]

Hi. I have a smooth and stable framerate (60 FPS) in the game almost all time, except for one case. When I come close and staring at any wall or crate or any relatively big non-transparent plane framerate drops drastically to about 30 FPS. Which is quite weird, as every game I played till now had the opposite effect (staring at wall => less polygons in frustum => higher FPS; look at open space => more polygons in frustum => lower FPS). That is also quite annoying, cause crawling in front of walls and crates is not uncommon in the game. There is no such problem with transparent objects and objects that don't cover much of a screen (like poles).
So my question is: why is it happens and how to fix it?

P.S.
Sorry for the english - it's not my native.

Here is my specs:
core i5 2500 @ 4000Mhz
AMD HD 6950 2GB @ 900/1375
RAM - 8GB
win 7 x64
Catalyst - 11.8
Catalyst settings is default, except for:
AF - 16x
VSync - on, unless app specs
AA mode - adaptive multisample AA

Also I have D3DOverrider with:
force vsync - on
force triple buffering - off

Game settings:
1920x1200
DX 11 on
FXAA High
Shadows: Soft
DOF: High
SSAO: High
Post Processing: on
Texture Filtering: 16x anisotropic
VSYNC: on
Triple Buffering: off
Tessellation: on

[Syvere]

Turn SSAO down to normal. That fixes it and you get more pronounced SSAO like in console versions.

[rumisterx]

It helped. Thanks.
Still AO in game looks somewhat weak either on high or normal.