After installing a e3d v6 head in my MP Mini, I noticed the amount of space to let the air crossing the heatsink out the back was minimal. I could feel backwash from the fan so air was definitely not flowing unobstructed.
This is a remix of a 40mm fan duct, but I cannot find the original. I have printed many ducts but none fit the e3d v6 clone as well as this duct. The design is excellent and prints perfectly with no supports or anything.
So to allow more air to flow over the heatsink and out the sides, I created 2 remixes with exhaust ports on the sides. One with 3mm circles, one with a 3x15mm rectangle hole. This allows you to use the popular e3d mounts for the MP mini while allowing for plenty of air to cross the heatsink.
I printed in PLA with 100% infill and have had no problems with heat up to 220c. I use a 12v 40x30mm fan running on 5v. Runs very quiet and cool.