We as anglers put our bait on clear spots primarily, for rig efficiency and in our minds thinking that's where the fish need it to be to feed on it. Carp are masters of their own environment though and can feed where they like, when they like. So from clean gravel, clay spots, silt in varying depths , in the weed and of course in the water column itself. By watercraft and observation of any food being excreted by a carp that you catch you can get an idea on where they are feeding predominantly. In my opinion there are definitely times when fish prefer to feed on gravel, on/in silt etc. If you can work this out on your lake then it makes the puzzle easier to fit together.
I've fished a couple of lakes in the past that were full of gravel bars/plateaus, silt gulleys and weedy areas. Without doubt in my own fishing the gravel spots in these lakes or the weed were the places to fish in the warmer months. Though at night time better results were achieved by fishing where the gravel met the silt. Autumn time was definitely the silty areas/clay spots that done the majority of the fish for me.