I have tried googling and couldn't find anything on this seemingly simple topic. Should I mount my fans so that they are directly against my mesh front panel? Or should they be on the inside with a few centimetres of distance? https://ibb.co/Hgj1LtN
There are 2 primary reasons. The first is the pressure issue sucking air directly through any restriction, in your case mesh. The other is that it moves the fans slightly closer to the other components so the air speed will be slightly higher, also, it will make slightly less noise due to not sucking air through the mesh and slightly further from your ears.
Gamers Nexus has covered this pretty extensively, their YouTube channel is great. I can't remember which video this was specifically covered in, it was within the last few months, a glass fronted case I think.
Might be easier to fin it on their website, all reviews are written up as well.