Consider giving the inner portion or the entire cutout a 'D' configuration, with the flat side down. The flat side should be parallel to the top of the fuselage when the blade is at it operational pitch. This should minimize the cyclic changing of the air density between the blade roots and the roof of the fuselage and thereby reduce vibration and noise.

It might be advantages to have no cutout and bring the blade in tight to the hub. This might include bringing the leading and trailing edges in further than the portion of the hub that contains the feathering bearing. The reason is that in fast forward flight, with the pusher prop providing a large portion of the propulsive force, this additional 'wing' will provide additional lift on the advancing and retreating side. In addition, it will shorten the blades thrust moment arm slightly and reduce the root loss effect.

This thought is particularly relevant if the root skin rotates about the spar and has and external root pitch link.