The 100-30-30 rule (originally 100-40-40 rule) is considered as a reasonable method for spatial response combination replacing the- more accurate- SRSS method.

Giving credit to the explanations of "Provisions", it appears that a vertical seismic load of 0.2*SDS wouldn't be applied in a SRSS method, neither be further amended by coefficients as 0.3 or 0.4 in combinations.

As a suggestion, I think it is worth also to implement in Caesar the vertical ground motion spectra definition that is given in the Chapter 23, Vertical Ground Motions for Seismic Design” starting with 2009 edition of the NEHRP provisions. That one may be considered directly in SRSS or "equivalent" combinations, instead using the commonly ratio of V/H = 2/3 in engineering applications