If any corporation believes that the method of allocation or apportionment hereinbefore prescribed as administered by the Department has operated or will so operate as to subject it to taxation on a greater portion of its Virginia taxable income than is reasonably attributable to business or sources within this Commonwealth, it shall be entitled to file with the Department a statement of its objections and of such alternative method of allocation or apportionment as it believes to be proper under the circumstances with such detail and proof and within such time as the Department may reasonably prescribe. If the Department concludes that the method of allocation or apportionment theretofore employed is in fact inapplicable or inequitable, it shall redetermine the taxable income by such other method of allocation or apportionment as seems best calculated to assign to the Commonwealth for taxation the portion of the income reasonably attributable to business and sources within the Commonwealth, not exceeding, however, the amount which would be arrived at by application of the statutory rules for allocation or apportionment.