Just a couple of observations on the design for the underside fan mounts.
The cooling fan can not be changed to the back. The jumper and the connector for the cooling fan are there. As well as the heater connector. So the cooling fan and cover won't allow for it to go there.
When looking at the left side of the board, the Termistor connector is in the way and won't allow for connection. That thing has a pretty good drop on it. That's like a good 20mm from the top of the PCB to the bottom of the clip there.
I really believe that about the only place that you'll be able to put that type of fan is in the right side of the board. And even then you'll have to turn the cooling fan a smidge.
I may be looking at it all wrong too. But that is what I found when I printed them out and tried them.
Great work so far there guys.