Subject to § 5-1004 of this subtitle and except as provided under § 5-1005 of this subtitle, an insurer may not retain a risk on any one subject of insurance, whether located or to be performed in the State or outside of the State, in an amount exceeding 10% of the insurer’s surplus to policyholders. An insurer’s surplus to policyholders shall be determined at the time a risk is assumed from the more recent of: the last sworn statement of the insurer on file with the Commissioner; or the last examination report of the insurer. In determining the amount of risk retained by an insurer, a deduction shall be made for reinsurance ceded by the insurer for which credit is allowed under § 5-904 of this title.