For the purposes of this Act (a) the value of the interest of a lessor or a mesne lessee in the land value of the land is the fair present value of the net ground rent receivable by him or her for the unexpired term of the lease, together with the fair present value of any reversion of the land to which he or she is entitled, exclusive of the structural improvements; and(b) the value of the interest of a lessee, other than a mesne lessee, is the land value of the land less the value of the interests of the lessor and any mesne lessee, as determined under this section.