Like @Shiv_P said, arma sinks you into the ground at larger distances, to emulate being obscured by grass,
and its alot more then just a visual effect thats an annoyance for the following reasons:
1. for close range, the grass can be a good emergency cover, say you're alone, and 3 people walk up to you, with nowhere to hide, you decide to just stay prone in the grass, since that grass is there for everyone, regardless of video settings, theres a chance they wont notice you and you can get away from there or better yet, find the right moment to strike and kill them.
2. for