I am learning I almost think the faster the crop moves through the rotor/cage the better. It keeps the crop mat thin and the seeds can separate easier. If you generally have tough straw conditions I don't think you want any reverse bars. If your straw is generally dry and breaks up easy you could get away with them. You would likely get more shoe load though. I put an f2 bar right in the bottom of the belly of the cage when I put in the channel helicals and I've never run without it. I think if you felt the crop mat was moving too fast there's enough room to install two of them to restrict flow. I get a bit of build up of straw on the top of the cage and on the right hand side upper rear of the cage in wheat. I also install covers across the section of cage above the concave otherwise I get straw build up around cage. We grow barley, lentils, and canola also and I get no build up at all from those crops.