Section 492. Ascertainment of amount of special assessment in certain cases

If a portion of a parcel of real property is subject to taxation
  pursuant to section four hundred twenty-a, four hundred  twenty-b,  four
  hundred  twenty-four, four hundred twenty-six, four hundred thirty, four
  hundred thirty-six or four hundred thirty-eight  of  this  article,  the
  amount  of  any special assessment to be levied on such portion shall be
  ascertained by considering the benefit to the property to be in the same
  proportion as the assessed valuation  of  the  taxable  portion  of  the
  property bears to the assessed valuation of the property.