Guilin Sun
Ansys Employee

The number of frequency points is to output how many resonant wavelengths. 

Does the change happen to the largest Q? did you check the resonant wavelength? 

For such devices if the periodicity does not change but only hole diameters change, you will make sure each period has exactly the same mesh, eg, you will need an override region with mesh size delta=period/N where N is an integer. However when both the diameter and peioidicity change it is challenge to have integer number of meshes. In this case you may need to use finer mesh along the direction of local periodicity.