Conn. Gen. Stat. § 12-218a

(b) If more than fifty per cent of the total gross premiums received during the income year by an insurance company taxable under this chapter consists of reinsurance premiums, any tax imposed by section 12-214 shall be imposed on the specified base apportioned to this state by multiplying such base by a fraction, the numerator of which shall represent the sum of (1) gross direct premiums, as defined in section 12-201 , received during the income year for insurance on property or risks located or resident in this state, plus (2) gross reinsurance premiums received during the income year in respect of property or risks located or resident in this state, and the denominator of which shall represent the sum of (A) total gross direct premiums received during the income year from all sources, plus (B) total gross reinsurance premiums received during the income year from all sources. For purposes of this subsection reinsurance premiums received in respect of property or risks located or resident in this state, whether or not otherwise determinable, may, at the election of the company, be determined either on the basis of the proportion which reinsurance premiums received from domestic insurance companies bear to reinsurance premiums received from all sources or, alternatively, on the basis of the proportion which the aggregate amount of gross direct premiums received for insurance on property or risks located or resident in this state by all the companies which ceded reinsurance to the taxpayer in the income year bears to the aggregate amount of gross direct premiums received by said companies from all sources.