The problem with the NACA duct is twofold. Firstly, it is exposed to the heated cabin on the back side which Dynon discourages in the install manual. The other item is that the engine heats the cowling surface from below and your cowling inlets may even backflow a bit at high speed which will give a potential error. My RV6 has the probe in the NACA (as installed by the previous owner) and it always reads too warm in flight. It is accurate while parked. It may work for you but I would try to avoid the NACA.
