This is an outdated design. That said, when I used this design, I didn't have any issues with it. This has been replaced by an openscad based design that automatically builds the parts based on what you choose for options. That does have the fan on the opposite side of one of the carriages that design supports. I would like to do the same thing with the i3 carriage and probably make that an option once at some point. That said, I've not had any issues hanging the fan off the front, other than visibility.

Aren't you worried about restricting the flow of air for the 30mm heat break fan? Perhaps mounting the print fan on the rear of the carriage would be better (as Prusa is doing in his latest design)? It would also allow you to see what is going on at the nozzles, they are hidden from view now.