Rate Limiting kicks in even before the quota limits are reached

Handler code is as follows which has maxAmount set to 50 and validDuration is set to 1s.

What I would expect from this setting is that the rate limiting should kick in only when there are are more than 50 requests/s. But, I am seeing that rate limiting kicks in at 15 requests/s itself. I am running in a minikube configuration.

Any idea why the behaviour is not on the expected lines?

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
# The first matching override is applied.
# A requestcount instance is checked against override dimensions.
overrides:
# The following override applies to ‘reviews’ regardless
# of the source.
- dimensions:
destination: helidon-quickstart-mp
maxAmount: 50
validDuration: 1s