I can confirm that the refractive index is correct, as it is the same for both mesh refinement options after meshing, monitored with the refractive index monitor.
Conformal variant 1:
 
Precise volume averaging (precision 11):
It is clear that the expected diffraction behavior of a sinusoidal grating is lost after meshing with "precise volume averaging".
As I would like to use the "precise volume averaging" mesh refinement for arbirarily shaped surfaces, it is unfortunately not an option to use a custom simulation object.
Is this an incompatibility between the importsurface2 function and precise volume averaging or can this problem be resolved by changing some settings?
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