Should the PSU Hover in Place?

My power supply is a couple millimeters above the bottom of the case. Is this normal, or should it be in contact with the bottom of the case? It is held in by screws but I'm not sure if this is normal or not for it to hover.
 
Solution
gotta love TechPowerUP and their VERY detailed reviews. yup, your PSU should be sitting on top of these rail bumps, so you'll have a gap between the bottom of the PSU and the slots in the case

casereardust.jpg
Well, my case has a sort of rectangular removable front bracket that the PSU screws into. According to the case manual, you remove the bracket and screw the PSU into the bracket outside of the case. Then you stick the bracket with the power supply attached into the case, and screw the bracket into the case.

There do seem to be there lumps or prongs underneath the PSU 2mm below it.