The larger tabs are desirable for their ability to produce large pitching moments, but without any significant penalty in terms of maximum lift. [Source ~ PHA p.273]

The greatest downwash will be when the upper blade is at azimuth 90º. At this location the tip of the upper blade will be directly above .75 R of the lower blade. There will be some reduction of the downwash's diameter at the lower blade. The striking of the downwash on the lower blade is not a desirable, there for it will be advantageous to keep the entire tab outside the .70 or .75 R of the blade.