Not a clue about what you'll see but I can say that the clearance to the duct is probably way too much. Ducted props work best if the tips are shaped to use the duct as a fence so the tip effects are minimized. So the tips should be cut off square (slightly arced to match the duct diameter actually) and the clearance to the duct should be no more than about 1/16 inch. Also you did not mention what the duct shape is. For best performance the duct should have an exagerated venturi shape at the intake side. 1/2 inch of duct before the prop sounds like it may work but then again it may not be enough at that point. There was some info in an old glow ducted fan article I read one time that had the ducted fan unit up above the wing and the guy found that with the sharp edged and short entry much noise was present and the thrust was poor. Adding a venturi intake lip ring added about 1/2 of an inch to the mouth to bring the lip to fan distance up to what appeared to be about an inch. This venturi and extended intake mouth length smoothed the airflow entering the fan and kept the turbulent blowback within the duct mouth where it could be re-swallowed by the fan rather than forming a tubulent area that pushed the incoming air away. I also suspect that you'll need a longer exit duct.

If this is important to you I would start by clipping the prop tips and sizing the duct to shroud the prop much more tightly. Play with some cheap GWS props if you do not want to cut up the Todd's prop. Also play with the duct length and prop placement within the duct. This is not cut and dry stuff where you can predict numbers. You'll get the maximum from playing with the parameters.