Thanks for the welcome and for the reply Copper_Dolphin, and that's a valid point: maintenance requires that you bring the bed down and remove the duct.
The use of the socks is mandatory (or any similar insulation) since the duct is very close to the hot end. This socks really does a good job, and also has the advantage that plastic doesn't stick to it I've been printing non-stop for 2days now with this solution and it has still not melted!
It's also true that the design could be larger at the end, it does restrict a little the airflow, but far less than all the ducts I've tried so far (and probably less than the photo you showed me I've tried similar design and the transition between the square tube and the tip literally kills the airflow, especially if there is nothing inside to guide the air on the sides). Anyway, it's always about compromises, and I didn't want to lose in printable space with a larger solution.
Besides, and for those who doubt about the 360 solution VS blowing on a single side: just do a print test with overhangs in every direction and you'll quickly see the difference! Out-of-the-box, I had serious issues with overhangs (solved now), so it was my focus when designing this duct.
If one wants to use it as a base design and modify it I can make the files available here
I'll check Facebook....