Thanks for the pic links, after looking at those and the ps ones at <A HREF="http://www.vr-zone.com/reviews/PSU/Vantec/VAN-520A/" target="_new">VR-Zone</A> it makes the puzzle more clear. From what I see, you have a few options.
1. Remove the grill that touches the top compartment - no damage should happen to the fan since the slim clearance prevents foreign objects from getting in there. That would provide 1-2mm of clearance sans grill.
2. Disable that fan altogether and remove the grill. Airflow would likely be better, as it would be pushed out in a direct line.
3. (my choice)Fire up the dremel and do some custom cutouts. Aluminum is very easy to cut, grind, polish into a pretty cool custom case. To really enjoy the benefits of your nice ps, two cuts need to be made. I would even replace the factory grills with some aftermarket bio-hazard grills or aliens.
It's too bad Lian-Li did not take into account the airflow issues when they designed the inverted case. If you lived near me, I'd do the work for you for a beer.
<font color=green><b><i>Lizards</font color=green></b> do <b>not</b> taste like <b><font color=yellow>chicken</font color=yellow></b>,<b> <font color=yellow>chicken</font color=yellow></b> tastes like <font color=green><b>lizard.</b></font color=green></i>