Whenever I see my fish congratulate in an area of the tank where there is flow as opposed to a clam area the first thing that pops to mind is O2 levels. I have alwasy felt that if O2 levels are above 7 PPM my fish actually prefer calm areas to current. When O2 level drop below 6 PPM I can tell just by the way the fash are acting.
A true dead area is usually indicative of collecting and congregating waste on the bottom, only them to I adjust my flow nozzles.