Frustrum culling and Gpu instancing.

I've been messing around with GPU instancing latley to see how it can improve the preformance of my game. When I have multiple objects on the screen with a shader that makes use of instancing the "Saved by batching" stat increases (And the tris and verts). This happens even if the objects are far away from the frustrum of the camera. Im starting to belive that frustrum culling does not take place when using instancing. Am I right? Can I manually add frustrum culling? How?