And where the mill or mills aforesaid, with the rights of thirlage thereto annexed, are let to tenants under tacks or leases, the annual payment in grain or money so as aforesaid to be paid as a commutation or equivalent for the right of thirlage annexed to such mill shall and the same is hereby declared to be payable during the term or currency of such tack or lease to the tenant or lessee of such mill or mills, and such annual payment shall be to such tenant or lessee, tenants or lessees, full compensation for or in lieu and satisfaction of all multure, mill services or other rights or servitudes pertaining or incident to the said right of thirlage let to him or them by such tack or lease, such tack or lease or any condition or prestation therein contained notwithstanding; and where the lands of the servient tenement or estate thirled are let in lease to tenants, and the proprietor shall pay the annual commutation or equivalent, the lessees shall in that case be obliged to make payment to the proprietor of a proportion of the said annual commutation or equivalent, corresponding to the rent of the lands let in lease compared with the total amount of rent payable by the whole lands thirled, and that the said proportion of the said annual commutation or equivalent shall be recoverable by the proprietor in the same manner in which he is entitled to recover his rent.