We report the first synthesis and computational study of Sc3N@C78(CF2) - an analog of the previously reported Sc3N@C80(CF2) with a less common carbon cage whose chemical properties presently remain far less studied. Sc3N@C78 appears to be considerably more reactive toward CF2 addition than Sc3N@C80 and somewhat more reactive than C60. Even though the less symmetric D3h(5)-C78 carbon cage offers far broader opportunities for isomerism than Ih-C80, CF2 addition to Sc3N@C78 proceeds regioselectively, similarly to other common fullerene reactions. A DFT survey of the thermodynamic and kinetic aspects of CF2 addition demonstrates that the regioselectivity is controlled kinetically.