The Commission shall determine the percentage that an occupational disease contributed to the death or disability of a covered employee when: the occupational disease is aggravated by another disease or infirmity that is not compensable; or the occupational disease accelerates, aggravates, prolongs, or in any way contributes to a disability or death from a cause that is not compensable. The compensation payable shall be reduced to the percentage of the compensation that would have been payable if the occupational disease had been the sole cause of the death or disability that equals the percentage that the occupational disease contributed to the death or disability, as determined by the Commission under subsection (a) of this section. As may be in the best interest of the covered employee under the circumstances of the case, the Commission shall reduce the compensation to the percentage required by paragraph (1) of this subsection by reducing: the number of weekly or monthly payments; or the amount of the payments.