It seems that the AI is able to shoot and see through bushes and grass, I often get shot by AI whilst laying in the grass, I can't see them from first person but they see me and kill me.
I've had the same problems with shrubs, bushes and trees, many times now I've been killed as the AI pinpoints and shoots me despite crouched or laying behind a large bush and having a tree obstructing their view.
On one occasion, I was on top of a hill, the AI gunner was below me, in first person I was completely covered by grass and could not see the enemy AI, however he saw me and repeatedly killed me in various similar positions.