Well, the card actually performs better in the orientation where half the vapor is going down and wicking back up, and worse in the orientation where it's flat.

But the bigger issue here is not the way orientation affects performance, but that defective cards seem to be hitting dryout. At that point a combination of not-enough-liquid and hot wick means that the liquid isn't making it back to the heat source before it boils again, and performance plummets.