A mod of the excellent Meshify S2 bottom plate by fallennae.
This version allows for a 140mm fan to be mounted in the lower position of the front panel, closing the gap with an upward scoop that will direct the airflow toward GPU/CPU and closing the PSU tunnel.

NOTE: The front tab should have a tapped hole to fix using the screws provided with the case (like the default metal plate). The thread is not quite M3, although an M3 screw will fit through the hole in the front panel.
I decided to not print the hole, since my printer would never do a good job. Instead, it is best to position the plate then drill the hole in situ. The screw is completely optional, as the part will sit snug even without it.

NOTE2: The fit is tight. With a Silentwing Pro4 there is barely any space left. In fact, mounting the fan requires removing the middle fan as well, inserting the shroud, sliding the bottom fan from the center, lowering it into position, then installing the middle fan.

NOTE3: There are 2 different versions of the design. The difference is the funnel lenght. I find version 2 to work better and look nicer.