I have found that the slider type floats work the best for me in deeper water. I also really like the dacron bobber stops, not the plastic ones ( they tear up your line).. Keep moving the bobber stop up on your line until the bobber jerks every few seconds while progressing through the drift. ( you know your on the bottom) then move it back down six inches. this way you know your presentation is six inches above the bottom ( in the strike zone).
Another trick is keeping line out of the water. If you let the line "drag" the current will pull your line and bobber speeding up the drift. Try mucilin on the line ( flyfishing floatant) and make upstream mends every so often. This will eliminate "pull".
I fish the EF Lewis quite a bit so Ill probably see you on the water sometime. Good luck!