You need to change lures, both in finish, weight and style if the ones out there are not working doing so every half hour. Varying speed will sometimes trigger bites as you speed up or slow down. As to targeting fish I try to concentrate on the middle column as these are usually the most active. If I see numbers near the bottom I will slow to idle foreward for about 20 seconds or so so KOs and Cleos can drift down close to their level. This won't work with HotnTots or WiggleWarts as they float but you know that. My leads on these flat lines are always 80' to 100'. Hope this helps.