(a) At the request of the insurance carrier, the commissioner may order that impairment income benefits and supplemental income benefits be reduced in a proportion equal to the proportion of a documented impairment that resulted from earlier compensable injuries.
(b) The commissioner shall consider the cumulative impact of the compensable injuries on the employee’s overall impairment in determining a reduction under this section.

(c) If the combination of the compensable injuries results in an injury compensable under § 408.161, the benefits for that injury shall be paid as provided by § 408.162.