I configured rate-limiting correctly according to the istio tutorial, and it worked. But when I lowered the limit, it seemed that rate-limiting had not changed.Here are all my configuration files. I hope you can give me some help. Thank you very much.

apiVersion: config.istio.io/v1alpha2
kind: handler
metadata:
  name: quotahandler
  namespace: istio-system
spec:
  compiledAdapter: memquota
  params:
    quotas:
    - name: requestcountquota.instance.istio-system
      maxAmount: 500
      validDuration: 1s
      overrides:
      - dimensions:
          destination: productpage
          source: "10.28.11.20"
        maxAmount: 500
        validDuration: 1s
      - dimensions:
          destination: productpage
        maxAmount: 500  （Here I increased the number of requests per second.）
        validDuration: 1s
---
apiVersion: config.istio.io/v1alpha2
kind: instance
metadata:
  name: requestcountquota
  namespace: istio-system
spec:
  compiledTemplate: quota
  params:
    dimensions:
      source: request.headers["x-forwarded-for"] | "unknown"
      destination: destination.labels["app"] | destination.service.name | "unknown"
      destinationVersion: destination.labels["version"] | "unknown"
---
apiVersion: config.istio.io/v1alpha2
kind: QuotaSpec
metadata:
  name: request-count
  namespace: istio-system
spec:
  rules:
  - quotas:
    - charge: 1
      quota: requestcountquota
---
apiVersion: config.istio.io/v1alpha2
kind: QuotaSpecBinding
metadata:
  name: request-count
  namespace: istio-system
spec:
  quotaSpecs:
  - name: request-count
    namespace: istio-system
  services:
  - name: productpage
    namespace: default
    #  - service: '*'  # Uncomment this to bind *all* services to request-count
---
apiVersion: config.istio.io/v1alpha2
kind: rule
metadata:
  name: quota
  namespace: istio-system
spec:
  # quota only applies if you are not logged in.
  # match: match(request.headers["cookie"], "user=*") == false
  actions:
  - handler: quotahandler
    instances:
    - requestcountquota

At first, I configure it directly.

- dimensions:
Destination: product page
MaxAmount: 1
Valid Duration: 5S

Rate-limiting works well. When I configure:

- dimensions:
Destination: product page
MaxAmount: 500
ValidDuration: 1s

The request will still return 429 in a short time，configuration (500/s) should be unrestricted at this time.During the test, I visited k8s product page service IP directly, such as curl 10.233.5.240:9080/product page.

I hope you can tell me why. Thank you very much for your answer.