Monthly expenses are not considered at all. They don't care how much your mortgage payment is, what your debt payments are, or if you live in an area where the cost of living is much higher than others.
Its a pure numbers formula, plain and simple.
Adjusting the amount of aid is the job of the financial aid department of the school your child will attend, and often the ONLY extraneous expense they will consider in adjustment is if you have significant medical costs or a very unusual living situation (supporting other family members who may have significant medical issues).
The estimated family contribution (EFC) that is computed from the FAFSA will tell you whether you qualify for Federal grant money (again...strictly based on the EFC FAFSA spits out). Any other aid is really determined by the school.
Two things you can know for sure: your EFC will most likely end up much higher than you expected, and having an EFC of $0 does NOT mean your child will go to college without paying anything.