Ducted fans need inlets sized to approximately 95%-110% of the Fan Swept Area (FSA) with an exhaust outlet sized to approximately 75% 85% FSA. Choking down airflow at the exhaust, increases exhaust velocity. This in turn will increase top end speed of the aircraft. There is, however, a point of diminishing returns: choking down the exhaust too much will back pressure the fan resulting in degraded performance. Additionally, a larger outlet area will increase the static thrust of the system, but lower the top end speed of the aircraft.

For more information on the general rules of ducted fans, visit [link=http://www.jethangar.com/]Jet Hangar International[/link].

Typically, when using scale intakes on an EDF system, cheater holes are used to create sufficient thrust on take-off. My recommendation would be to create a cheater hole (or holes) in front of the DF and start there. Once you determine that the plane has sufficient take-off power, you can then start covering the cheater hole(s).

Good luck!