SNS maxReceivesPerSecond throttle being ignored

Hi there, we're facing an issue with SNS whereby the maxReceivesPerSecond value on the subscription (HTTPS) is being completely ignored. Our traffic logs in Cloudflare show 1.46k requests to our SNS endpoint within 1 minute despite configuring a maxReceivesPerSecond value of 5 (therefore meaning a maximum of 300 requests per minute).

We've verified that disableSubscriptionOverrides is false on the topic itself, so as far as we're aware the throttling should be working? Can anyone advise please?

Topic Delivery Policy

{
  "http": {
    "defaultHealthyRetryPolicy": {
      "minDelayTarget": 20,
      "maxDelayTarget": 600,
      "numRetries": 10,
      "numMaxDelayRetries": 2,
      "numNoDelayRetries": 0,
      "numMinDelayRetries": 0,
      "backoffFunction": "linear"
    },
    "disableSubscriptionOverrides": false,
    "defaultRequestPolicy": {
      "headerContentType": "text/plain; charset=UTF-8"
    }
  }
}

Subscription Delivery Policy

{
  "healthyRetryPolicy": {
    "minDelayTarget": 20,
    "maxDelayTarget": 600,
    "numRetries": 10,
    "numMaxDelayRetries": 2,
    "numNoDelayRetries": 0,
    "numMinDelayRetries": 0,
    "backoffFunction": "linear"
  },
  "sicklyRetryPolicy": null,
  "throttlePolicy": {
    "maxReceivesPerSecond": 5
  },
  "requestPolicy": {
    "headerContentType": "text/plain; charset=UTF-8"
  },
  "guaranteed": false
}