First, stand on the ledge outside palace:
Position yourself facing the dark dot on the block beneath the pillar second from right.
Then turn around and position your crosshair in between the dark marks on the parapet. Your crosshair should be vertically above the lower mark, and should follow the direction of the mark on the side. If you aim slightly lower (but still above the lower black mark) it should be fine. There is much less tolerance if you aim higher, however.
This is where the smoke should land:
