I have to say...
I've never known the PSU to exhaust through the bottom? The two PSU's I have exhaust air at the rear, where the mains plug is connetced, and suck in thorugh the bottom. And after checking their website and looking carefully at their PSU fan blades those fans are supposed to suck air into the PSU and expell it through the mesh at the rear.
So check that out first.
Also, as mentioned already, see if you can rotate the CPU heatsink 90 degrees clockwise.
And fit a fan on the front of the case underneath the Hard Drive caddy.
If you do fit a fan on the front underneath the hard drive caddy then block the PCI slot holes.