There's lot of opinions about pods and refugiums...
Some say a refugium under the tank results in virtually no pods being transported from there to the display tank, stating there's no good reason why a pod would want to be near the suction of a drain. If that's the case, why would an above the tank refugium be any different? It still has a drain that causes suction.
Others claim pumps kill pods, while even others have stated they've had small fish take the ride from their display tank to their sump / refugium and get pumped back up to the display, so they believe that pods aren't killed by pumps if their fish haven't been.
Personally, our refugium is under our tank. If pods are making it up to our display, great. If not, I'm not really that concerned about it. There's plenty of LR in our display and I can spot pods anytime I want. For me, the refugium is more important for nutrient export (growing macro algae) -- any pods making it from there to the display is just an occassional bonus.