For each regional school district, a state share shall be computed and multiplied by the reference year cost, as defined under § 16-7-16(11), of the basic program, as defined under § 16-7-16(3). The state share shall equal two percent (2%) for each grade so consolidated for the first two (2) years of operation, diminishing thereafter by one-fourth of one percent (¼%) per grade per year, but in no event shall the increased percentage be less than eight percent (8%); provided further, that the individual communities in the Chariho regional districts shall each receive the applicable increased percentage of those grades serviced by the regional school district. Reimbursement payments as calculated under this section shall be made in accordance with the monthly distribution defined under § 16-7-20(c).