Nice design and useful part
I get how you have this mounted, but it is actually the worst idea ever for a heatsink and fan. You aren't heat sinking anything and you are blocking the fan. the fins are the wrong way and you don't have intimate contact. If you left it off, it would do the same amount of cooling.
No, actually its working like a charm ... the part doesnt obstruct the air flow. I've tested with a termomether and its coolign pretty well. The part is just to allow me to change the filament with less effort.