Physics list per region

_Geant4 Version:_11.2.1
_Operating System:_linux
_Compiler/Version:_g++ 13.1.1
_CMake Version:_3.26.4

I want to set single scattering physics only with the target in my Rutherford scattering simulation, living Em_opt4 in World and detector.
i declared my physic in my physics list class

RegisterPhysics(new G4EmStandardPhysics_option4());

And in my run.mac I set

/process/em/AddEmRegion TargetRegion G4EmStandardSS

But this put the single scattering in everywhere. Does this not work like that ?

Did i do something wrong in the set up ?