It does look like the case was designed for a PSU to lay flat on the four feet, but then there is an opening in the back.
Just purchased a Thermaltake 850W Smart Bronze series and the screws line up, so my guess it will be slightly raised to avoid wobbling.
I purchased a 1000w Seagate SS1000XP Platinum power supply to go in my Thermaltake X71 case, but it was not tall enough to fit the screw holes.
Can anyone recommend a power supply that would fit the X71 case?