What are the endpoints of Amazon S3?
Looking here you can get a list on the terminating points of s3 that might help: https://docs.aws.amazon.com/general/latest/gr/rande.html#s3_region
Another solution can be to create a s3 endpoint inside the same VPC of your K8S cluster and use that name to restrict the access with private IPs rules. see https://docs.aws.amazon.com/vpc/latest/userguide/vpc-endpoints-s3.html for a detailed documentation on it.