Hi @TMcCorvie,
I would think that if you did a helical refinement with D1 symmetry, you should symmetry expand with the same D1 + helical symmetry parameters as the helical refinement, and then use the symmetry expanded particles for a C1 local refinement. D1 and C2 are both 180º rotational symmetries around an axis, but D1 is around the dyad axis (y in cryoSPARC), whereas C2 is around the z axis, so they aren’t the same.
Best,
Michael