if the @Webservice is on the SEI, the @Webservice on the SIB is ignored
This is correct when it comes to which methods are exposed in the webservice.
But... for the attributes/elements of the @Webservice annotation it is a bit different (and tricky!)
This is from the specs JSR-181:
3.1 Service Implementation Bean
The implementation bean MAY reference a service endpoint interface by using the @WebService.endpointInterface annotation. If the implementation bean references a service endpoint interface, it MUST implement all the methods on the service endpoint interface. If the implementation bean references a service endpoint interface, that service endpoint interface is used to determine the abstract WSDL contract (portType and bindings). In this case, the service implementation bean MUST NOT include any JSR-181 annotations other than @WebService and @HandlerChain. In addition, the @WebService annotation MUST NOT include the name annotation element.
3.2 Service Endpoint Interface
The service endpoint interface MUST NOT include the JSR-181 annotation elements portName, serviceName and endpointInterface of the annotation @WebService.