Drippers with top air holes almost don't - simply because you almost never hold your mod upside down. With side air hole drippers - the vast majority of the drippers on the market - the problem can be mitigated, depending on the particular model, how high the holes are, how deep the well is, wicking, and how you handle the thing. But clearly they leak, given the right circumstances. As for bottom air hole drippers, gravity and plain logic makes them sure leakers, whatever you do about it.
Me, I only use top air hole drippers nowadays: it's just too comfortable to always handle dry vaping hardware. Too bad there aren't too many RDAs of this type on the market.