Yes, you are right. The PSU is installed upside down and there is a fan grille in the base plate, right under the installed PSU.
The PSU Mount Area is pictured in the servethehome-review.
The reasons why i installed the PSU upside down are:
- As you mentioned, there is not much space under the base plate. Maybe its enough space for a good air flow for the first time. But i am not a big fan of this kind of drilled fan grille. I think sooner or later a drilled fan grille will be clogged with dust espacially if its located in the base plate and if your system is running in a home-environment in or next to rooms where people live.
- The second second reason why i installed the PSU upside down is: The PSU is generating additional airflow under the HDD-bays. This removes warm air to prevent a hotspot, which possibly could affect HDDs in the HDD-bay and possibly the areas of the mainboard which are located next to the PSU (Ram, and maybe the M.2 SSDs). Its not a problem for the PSU to transport warm air: My PSU can handle up to 500Watt. The average powerconsumption of my setup is at 70-80watt effective, so there is enough thermal budged left to operate the PSU in a safe condition. The fans of the PSU are running at low speed, which would not be the case if the PSU would have thermal problems, because they a temperature controlled.