In certain areas of the state where due to sparsity of population and distance between centers of population, an area high school cannot be established to serve as many school districts or pupils as would otherwise be standard, the receiving districts in any such small authorized regional enrollment areas as may be approved and established hereunder for a high school, in addition to the aid granted in N.H. Rev. Stat. § 198:19, shall be paid annually by the state board, from a fund appropriated by the general court, special supplemental aid in such proportionate amounts from the fund thus made available as may be determined by the state board, in accordance with the relative need of such smaller area high schools, for the purpose of faculty improvement. Such special aid shall be fairly and equitably apportioned by the state board as of June 30 in each year and paid to the eligible receiving districts in the succeeding fiscal year based upon conditions prevailing in the preceding fiscal year. Such special aid shall be deducted from current expenses of operation before tuition is calculated.