Some CSS Profile schools do NOT add back in the pre-tax contributions to available income, while others may do so, or do a portion of. I have been told that several schools will add back in any amount over 6% of income - typically what a lot of companies match on.
The FAFSA means nothing for most CSS Profile schools - other than to identify Pell grant eligibility since that is the same for all schools, using the FAFSA formula.
My pups, at Columbia and Stanford, which both use the CSS Profile, end up with EFC far lower using the school’s CSS Profile formula, than the pure FAFSA would have calculated.