Thanks for the feedback!
My thinking in this design was that the fan would be moving air to the sides of the heatsink and that making the case wider than it absolutely needed to be in addition to keeping the mesh pattern extending all the way to the sides would provide some room for the hot air to escape upwards. Although this isn't a positive air flow design (although I did play with that with a previous design – and you can see a peak of it in one of the blue prototypes in one of the images), the fan should be very close to the top mesh to pull in air external to the case.
I am very interested in thermal performance and will make modifications to the design if it isn't working out. Let me know how it goes for you too – I'm curious how hot this thing will get. :)