JDE 9.2 Non-Statutory Tax Exempt

Can someone please confirm the proper way to mark an employee as federal income tax exempt? In the past, FICM=2, but now we are noticing that taxable wages are zero because gross is moved into excludable. I believe that flat zero on tax overrides marked the employee as statutory. Are we going back to 99 exemptions? I'm finding conflicting information. I've also seen recommendation to use FICM=X but that doesn't seem right either.

Thanks in advance!