HTTPRouteFilter's urlRewrite does not take effect under backendRefs

The urlRewrite of HTTPRouteFilter does not work under backendRefs, but it works under rules. Is this as expected?

apiVersion: gateway.envoyproxy.io/v1alpha1
kind: HTTPRouteFilter
metadata:
  name: backend-1-credential-injection
  namespace: envoy-gateway-system
spec:
  urlRewrite:
    hostname:
      header: x-custom-host
      type: Header

apiVersion: gateway.envoyproxy.io/v1alpha1
kind: Backend
metadata:
  name: backend-node3-fqdn-1
  namespace: envoy-gateway-system
spec:
  endpoints:
    - fqdn:
        hostname: application-1.hardybrown.com
        port: 65201

-------not work config----

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: httprouter-to-node3
  namespace: envoy-gateway-system
spec:
  parentRefs:
    - name: eg
  hostnames:
    - "envoy.hardybrown.com"
  rules:
    - backendRefs:
        - group: gateway.envoyproxy.io
          kind: Backend
          name: backend-node3-fqdn-1
          filters:
            - type: ExtensionRef
              extensionRef:
                group: gateway.envoyproxy.io
                kind: HTTPRouteFilter
                name: backend-1-credential-injection
      matches:
        - path:
            type: PathPrefix
            value: /

-------work config----

apiVersion: gateway.networking.k8s.io/v1
kind: HTTPRoute
metadata:
  name: httprouter-to-node3
  namespace: envoy-gateway-system
spec:
  parentRefs:
    - name: eg
  hostnames:
    - "envoy.hardybrown.com"
  rules:
    - backendRefs:
        - group: gateway.envoyproxy.io
          kind: Backend
          name: backend-node3-fqdn-1
      matches:
        - path:
            type: PathPrefix
            value: /
      filters:
            - type: ExtensionRef
              extensionRef:
                group: gateway.envoyproxy.io
                kind: HTTPRouteFilter
                name: backend-1-credential-injection