Using copies of physical volume in single sensitive detector

Hi everyone
I simulated a scintillator detector and then counted the optical photons produced using the sensitive detector class. For a single sensitive detector, it is working perfectly fine, then I copied the volume placements to make two detectors, and the logical volume is the same. After doing this, the sensitive detector counts way fewer photons. I didn’t understand why it is not working properly as it did with one detector. I am attaching a code snippet of defining the volume and sensitive detector.

    // general positions
    G4ThreeVector positionReflector = G4ThreeVector(0.*cm, 0.*cm, separation);
    G4ThreeVector positionReflector1 = G4ThreeVector(0.*cm, 0.*cm, -1*separation);
    G4ThreeVector positionScintillator = G4ThreeVector(0.*cm, 0.*mm, +0*mm);
    G4ThreeVector positionDetector = G4ThreeVector(0.*cm, 0.*cm, (.5*crystal_length - .5*detector_thickness)*mm);


 G4Tubs *solidReflector = new G4Tubs("Reflector", 0.*mm, (crystal_radius + reflector_thickness)*mm, (.5*crystal_length )*mm, 0.*deg, 360.*deg);
    G4LogicalVolume *logicReflector = new G4LogicalVolume(solidReflector, Aluminum, "Reflector");
    new G4PVPlacement(0, positionReflector, logicReflector, "Reflector", logicWorld, false, 0, true);
    new G4PVPlacement(0, positionReflector1, logicReflector, "Reflector", logicWorld, false,1, true);


    G4VisAttributes *visReflector = new G4VisAttributes(G4Color::White());
    visReflector->SetForceWireframe(true);
    logicReflector->SetVisAttributes(visReflector);
    
    new G4LogicalSkinSurface("ReflectorLogicalSurface", logicReflector, AluminumSurface);
                                                                       
    // scintillator
    G4Tubs *solidScintillator = new G4Tubs("Scintillator", 0.*mm, crystal_radius, .5*crystal_length , 0.*deg, 360.*deg);
    G4LogicalVolume *logicScintillator = new G4LogicalVolume(solidScintillator, LaBr3, "Scintillator");
    new G4PVPlacement(0, positionScintillator, logicScintillator, "Scintillator", logicReflector, false, 0, true);
    new G4PVPlacement(0, positionScintillator, logicScintillator, "Scintillator", logicReflector, false, 1, true);


    G4VisAttributes *visScintillator = new G4VisAttributes(G4Color::Red());
    visScintillator->SetForceLineSegmentsPerCircle(25);
    visScintillator->SetForceAuxEdgeVisible(true);
    logicScintillator->SetVisAttributes(visScintillator);

    fScoringEnergy = logicScintillator;

    // detector    
    G4Tubs *solidDetector = new G4Tubs("Detector", 0.*mm, crystal_radius, .5*detector_thickness, 0.*deg, 360.*deg);
    G4LogicalVolume *logicDetector = new G4LogicalVolume(solidDetector, LaBr3, "Detector");
    new G4PVPlacement(0, G4ThreeVector(0.*cm, 0.*cm, +(45*cm+.5*crystal_length + .5*detector_thickness)), logicDetector, "Detector", logicWorld, false, 0, true);
    new G4PVPlacement(0, G4ThreeVector(0.*cm, 0.*cm, -(45*cm+.5*crystal_length + .5*detector_thickness)), logicDetector, "Detector", logicWorld, false, 1, true);
    
    G4VisAttributes *visDetector = new G4VisAttributes(G4Color::Yellow());
    visDetector->SetForceLineSegmentsPerCircle(25);
    visDetector->SetForceAuxEdgeVisible(true);
    logicDetector->SetVisAttributes(visDetector);

    
    /////////////////////////////////////////
   
   
//phantom

G4Tubs *phantomsolid = new G4Tubs("phantom", 0.*mm, .5*25*mm, .5*6*mm, 0.*deg, 360.*deg);	
	G4LogicalVolume* phantomlogic = new G4LogicalVolume(phantomsolid,water,
														"phantom");
	
	//G4ThreeVector positionCrystal1 = G4ThreeVector(0.*cm,0.*cm,
       //                                           0.*cm);
	
	 new G4PVPlacement(0,G4ThreeVector(0.*cm,0.*cm,  0.*cm),phantomlogic,"phantom",
														logicWorld,false,0,true);
		

    fScoringOpticalPhotons = logicDetector;

    return physWorld;
}

void DetectorConstruction::ConstructSDandField()
{
    SensitiveDetector* sensDet = new SensitiveDetector("/sensDet");
    G4SDManager *sdManager = G4SDManager::GetSDMpointer(); 
    sdManager->AddNewDetector(sensDet);
    fScoringOpticalPhotons->SetSensitiveDetector(sensDet);

  

}