Smallies in the summertime usually stay between that 10-30ft range. They stay as deep as where the thermocline starts in any given lake. A good graph is the key to targeting deep water smallmouth. Mainly I look for drop offs where bait congregates and where bait is near the thermocline. Also near really deep weed edges and rock ledges are great also. Then again, you are in a natural lake. Not all smallies in natural lakes go deep, some do stay shallow depending upon the forage. If the forage is there, then the fish should be too!