It's somewhere written down in the comments here... But I added it to the thing description now:
I use and recommend Leo's Mistral 2 or the Anet A8's stock fan duct. With the Mistral you should rotate the heater block in a way that the shortest extent points to the fan.
(Another option would be to determine the offset in x, y, z direction of your beloved (semi-)circular fan duct to the nozzle and then insert them in the expert settings in the CUSTOMIZER to fit the mount!)