Base Year is the Most Important One!

It's AGI.  But you may have to add back untaxed incomes like 401k, 401b, etc.  My understanding the base year income sets the level and at later years just minor adjustment if your income is relatively stable.  Base year is thus critical.  If you have more mortgage then your monthy payment will be larger and thus the financial aid.  The higher the income, the lower the financial aid.  But the higher the taxes you paid, the higher the fincancial aid.