The sinking flourocarbon causes a lot of water resistance. You will be amazed at how much water just the line actually resists. If you are using it for your main line it will sink and it will cause your bobber to tip on its side. The FNF bobbers are designed so that just 1/16th of an ounce will make it stand up or tip over. Guaranteed that sinking flouro gives off more than 1/16th of an ounce resistance to make your bobber tip over. My bet is that if you make a cast and let it sit for a long period of time and don't move it that when you reel in the bobber actually will sink under the water a foot or so because of the sinking line. When I fish DEEP crankbaits I always use flourocarbon and will actually make the cast then let it sit for a few seconds up to 20 so the line will sink first and this will help pull DOWN the crankbait right off the bat to get it to the max depth quicker. Maybe it is only helps a bit but I do know it helps. One thing to remember on the FNF, you want the fly doing as little moving as possible and you don't want any un-natural movements. With braid as your main line it will float and the only action you are giving is to the bobber and to the jig. If you main line is sinking and your bobber is tipping or bobbing up and down the the jig is bobbing up and down in the water column which is not natural this time of year. Slow quivering movements are natural and if your bobber stays on top and just twitches slightly then the jig with twitch slightly as well. Just my opinion but I don't plan on changing anytime soon, just TOO much success doing what I do. Elnut