From the frame order matrix element graphs in test_suite/shared_data/frame_order/sim_vs_pred_matrix,
specifically Sijkl_iso_cone_free_rotor_in_frame_theta_x_calc.agr,
Sijkl_iso_cone_free_rotor_axis2_1_3_theta_x_calc.agr, and
Sijkl_iso_cone_free_rotor_out_of_frame_theta_x_calc.agr, it is clear that the symmetry of the order
parameter after 120 degrees causes the 2nd degree frame order matrix to be incorrectly estimated.
Therefore the S1 order parameter has been replaced with the original cone opening angle cone_theta.
All parts of relax have been updated for this large conversion.