That one is totally passive cooled. You see even a sticker on top of the SFP cage that may block one of the venting holes. I used a small 12V fan that is powered by byte tapping in on the 12V poser supply for my 4011…he is on diet you see.
I use plugs for putting screws into a wall and this one are small ones and the ends are just pushed into the slots of housing. The fan is very small and very light (20 gramm) so those two plugs pushed in hold it easily.
I have this one and there are different sizes: https://www.blacknoise.com/site/en/products/noiseblocker-it-fans/nb-blacksilentfan-series/50x50x10mm.php?lang=EN
A very small one and also thin and handles 24V: https://www.blacknoise.com/site/en/products/blacknoise-industrial-fans/blacknoise-nb-ip55-series/40x40x10mm.php
Stick on the left side to the front and suck air out or in and you will extra cool the cage of SFP a few centimeters inside. You can also put an extra fan(s) on top of the heatsink at back if that is really getting hot. I think that is not a problem and it a BIG heatsink.
Those copper pipes you see are heat pipes and they are very efficient in transporting heat from one place to an other. So bolting a extra fan on the top is not the first option to think about.
Video comparing a copper rod and a heat pipe and a heat pipe is just awesome. https://www.youtube.com/watch?v=OR8u__Hcb3k