A controlled participant’s IDC share for a taxable year is equal to the controlled participant’s cost contribution for the taxable year, divided by the sum of all IDCs for the taxable year. A controlled participant’s cost contribution for a taxable year means all of the IDCs initially borne by the controlled participant, plus all of the CST Payments that the participant makes to other controlled participants, minus all of the CST Payments that the participant receives from other controlled participants ...