45 C.F.R. § 800.104
(a) Phase-in. OPM may enter into a contract with a health insurance issuer to offer MSP options if the health insurance issuer agrees that:
(b) Partial coverage within a State.
(2) If an issuer offers both an MSP option and QHP on the same Exchange, an MSP issuer must offer MSP coverage in a service area or areas that is equal to the greater of:
(c) Participation in SHOPs.