Testing spice model for common mode rejection ratio?
Use this circuit (and equation) instead:


Source: https://www.analog.com/media/en/training-seminars/tutorials/MT-042.pdf

It should be easy to come up with resistors in spice that are matched (in real life not so much and so you should use the other circuit in the application note).

This has worked for me, if it doesn't work the model may not be that realistic.

Another note:
While the diagram shown in the OP has no ground on the 18V supplies, I hope that there was a ground between the supplies in the spice netlist. Otherwise spice would have a very difficult time finding the DC operating point and simulating, as al the voltages of that portion of the circuit would be floating, and the simulation wouldn't function very well. Supplies need to be referenced from ground, which I hope was done.