I'm on the mission where the bonus objective is to assassinate a few soldiers from around corners - so I hide on the corner, and then I whistle. Some soldier that wasn't even in my line of sight, nor closer than the one that was,, who was highlighted, hears it and comes searching - which of course, usually gives me away when I have to kill THEM instead.

...is there really no way to target the whistle? even an AOE target would be fantastic, because it wouldn't attract enemies that I can't even see, if I could direct it even a little.

...because this way, it's just silly, lol... plenty of other games managed to do it properly, like Shadow of Mordor...