I also use the Yamaguchi worm in 4" and pinch an inch off the head before I put it on the jighead. The curly tail is nice, I've had times when I've seen the fish and swung it in front of them and had them slam it. As for the depth to fish a jig below a float it comes with experience but from what I've seen you don't have to fish them very deep. I usually fish my jig around 2 feet in most holes and adjust from there. Some slots that you know are shallower you run it accordingly. The fish will usually move up quite a bit to hit them, as a general rule keep it a foot or so off the bottom and you'll get fish.