I catch most of my summertime gills suspended over deep water, roughly 1/3 to 1/2 of the depth of the water. (So, in 12 FOW, I'd expect to find gills from 4-6' deep.)

FWIW, years ago in the old Southern Outdoors magazine, I read about this guy who fished Kentucky and Barkley for gills. He would find the river channel and catch them suspended. (He used a fly rod, but spinning would work, too.)