Yes, I do agree with your explanation. Normally the effect on a real aircraft or even the average r/c model is extremely small and in some instances is beneficial for stability. My view is that a 3-D model has already the CG aft enough to make it marginally stable and the small contribution by the increase in pitching moment can turn the model toward negative stability. We did wind tunnel experiments with different wing crossections of same thickness and chord length and while keeping the same AC for each one it was found that there was a relation between position of max thickness and pitch sensitivity.