Subject to the limitations provided under s. 71.26 (3) (n), for each taxable year that a corporation has a net business loss carry-forward, as provided under s. 71.26 (4) or 71.45 (4), that was computed on a combined report for a combined group’s unitary business for a taxable year beginning on or after January 1, 2009, the corporation may, after using such net business loss carry-forward to offset its own income for the taxable year, use any remaining net business loss carry-forward to offset the income of all other members of the combined group on a proportionate basis, to the extent such income is attributable to that same unitary business.