Sometimes you just have to tip your hat. But of you are in a one on one and a player ducks behind cover, reposition yourself asap. Obviously toss a grenade if you had one, but change his/her sight line and angle. I do the quick snipe to others and it works most the time because the player just stands or run in the same line I saw them in when I went behind cover. Makes my job that much easier knowing where they will be. Making the angle difficult for your opponent is very helpful in a lot of situations. To the flanked scenario, if you aren't in a one on one but have a radar ping straight ahead behind a door or corner, don't just ads while waiting. Zoom in and out so you can see the radar quickly. Also, just know the situation. Meaning if you are entering an area know all the angles that can get you and try to be in the best possible spot. Hope this helps!