The problem with the fan is getting the volume of air across the evaporator coil, the coil has to be quite narrow due to its positioning , if a dash mounted AC is required a better solution is actually to replace the complete heater box , and add the evap coil inline with the heater coil, however cost is the reason it was not done that way by the retrofitters such as Diavia.
The under dash system , of course doesn't allow screen demisting either.
The MOD simply had an evap ceiling mounted , the condenser mounted in a side locker.