Most valueable information: If you have 20 ashes, the achievement text turns green.
I did not bother to check the exact position (I was a Hunter and already busy) but combat replay shows the following positions:
http://puu.sh/geKDs/c945d1d708.jpg
Top right red circle is 100% sure, Bottom left red circle not so much.
Also if you get the ashes debuff and you die, it still counts.
Proof for this information:
http://puu.sh/geKVt/40c1c3a544.png
As you can see in the previous screenshot this hunter is dead.