Depends on the lake and the primary forage. In lakes with good amounts of both deep and shallow areas I have found them in both. But I think that the ones that I caught shallow were keyed in on the forage there and likewise for the deeper ones. In other words, not every perch is going to be doing the exact same thing at the same time.
I will say that it seemed like the shallow ones were more agressive when they turned on, but they seemed more hit or miss.
jjT