The injection template ignores any user specified status port when configuring the readiness probe.  See here https://github.com/maistra/istio-operator/blob/maistra-2.0/resources/helm/v2.0/istio-control/istio-discovery/files/injection-template.yaml#L262-L270

It's also unclear whether or not the sidecar can be configured to use an alternate port for status, either through global proxy settings or status.sidecar.istio.io/port annotation.

Update: updating the port to anything other than 15021 or 15020 does not seem to work.