Well, it seems "un-normal" with the power supply on the bottom. If I let the PSU fan point up, it appears to have a greater vent area (but the PSU is upside down). On the flip side (no pun intended!), the fan outputs into a small void.
I installed the PSU with the fan facing upwards. There is a bit more of an opening there. Those fans are intake fans anyway. They bring cool air into the PSU and the fan on the back is an exhaust fan.
The P180 also has a fan in the center on the bottom of the case. Between the PSU and the HDD brackets. This fan is responsible for bringing in fresh air and pushing it to the PSU, were the PSU intake fan will then eventually have it exhausted out the back of the case.