Apparently the game knows when a player is hiding inside of a bush since enemy NPCs (ex. the Police) cannot target players doing that unless they get really close to it. Also, if I am not wrong, in singleplayer the player’s arrow icon on the minimap becomes darker when you are inside vegetation.
My custom radar script immediately marks players appearing on the FOV unless they are taking cover, but that is overkill since even a single pixel appearing on the screen inside of a bush results in the player’s position getting exposed.