Lu,
Sorry that I didn't specifically answer your question, but here goes:
If you push the stick forward in a robbie, or an S-76, the disk will tilt almost perfectly forward, even though those aircraft have phase mixing that is not 90 degrees. The phase mixing that they have is exactly what they need to make the cyclic behave as desired, and varies from 90 degrees because it must.
Delta three is the biggest contributer, but also blade Locke number is a driver, where the phase angle varies from 90 degrees because of the natural "spring"of the blade (a balance of the aerodynamic forces, and kinematic forces that determine the natural resonance frequency of the flapping axis).
Hope that helps!