Any sort of surface imperfection will catch tiny air bubbles, so loosening the bolts might not do anything except make room for more bubbles. This is one the minor advantages of cylindrical reservoirs - fewer corners.
Tilting the case might alter the liquid flow within the reservoir enough to sweep some of the bubbles out of their hiding spot (especially if you loosen the bolts slightly) but it might also cause air to be sucked back into the loop again. Not sure what else to try.
Sadly, the cost of the reservoir doesn't mean jack. For something that really only has one job - let air/water in, but only let water out, there are more than a few high-priced failures out there. Fortunately, I have friends who found the hard way, so I go to learn the easy way.
i7 2600K | ASUS Maximus IV GENE-Z | GTX Titan | Corsair DDR3-2133