What Aaron121 said. The bumps are the stand-offs, which is a giant, grounded slab of brass.
There is a central stud/pseudo-stand-off to help you line up your motherboard.
I'm using a 300R at the moment, and I was kind of shocked to discover that as well.
This, set me back too. Although that standoff that helps align the mobo is a life-saver. Was having a lot of trouble before I noticed it, then I had it down in seconds haha,