Notwithstanding any other provisions of law, the maximum allowable building area for each applicant district shall be reduced by the product of the maximum area per attendance unit calculated for each appropriate grade level and the number of pupils reported by the Superintendent of Public Instruction for that grade level pursuant to Section 42268. This reduction shall be calculated on the basis, at the district’s option, of either the district as a whole or the appropriate attendance area, as defined in Section 17041.