The socket position doesn't. The socket could be on the house side and have a true FCO. My M-400 a2 has a house side socket. I think the reflector is different from the house side and street side sockets. Plus its the reflector and angle that determines if it is a true FCO. The M-400 a2 FCO optics aren't angled, they are flat down, thats why the FCO and SCO look way different. they are similar on the M-400 r2 (FCO/SCO) because the bottom housing already has a flat angle even in SCO. Only the reflector is different in the pattern. The SCO/FCO have the same top housing and refractor doors. (M-400 r2) But different reflectors and one has flat glass and the other has a refractor.