Hi Dag,
Will be interested to hear the results of your test. I did something similar. Test procedure was to trim the model for level flight then fly knife edge to see the impact on the pitch.Wing incidence at +0.9 deg. No attempt was made to move the batteries so the CG didn't move much between tests.
In summary.
No cannaliser- slight pitch to belly that could have been fixed by moving the CG forward
Large canopy mounted cannaliser ( +1.5 deg incidence) gave a pitch to canopy that required 12% rudder to elevator mix to eliminate . Didn't want to move the CG back to fix.
Smaller mid height canopy mounted cannaliser. This was originally servo driven between -1 to + 2.5 deg incidence. + 2.5 reduced the R-E mix to 5%- other incidences resulted in more pitch up. Concluded that drag above the thrust line may be causing the pitch up so fitted the belly cannaliser at about + 1.5 deg incidence. This eliminated the pitch so no mixing at all now. Am just starting on a new model and plan to use a canopy cannaliser but will lower the wing by 10 mm to see if that helps. Bill