Kustomize how to replace only the host in Ingress configuration

I've got this ingress.yaml base configuration:

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  labels:
    sia: aza
    app: asap-ingress-internal
  name: asap-ingress-internal
  annotations:
    kubernetes.io/ingress.class: "nginx-external"
    nginx.ingress.kubernetes.io/use-regex: "true"
spec:
  rules:
    - host: the-host-value
      http:
        paths:
          - path: /asap-srv-template/(.*)
            backend:
              serviceName: asap-srv-template
              servicePort: 8080

And want to replace the spec.rules.host value only (and keep all http.paths as is.

So I create a env-var.yaml like this :

apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  name: asap-ingress-internal
spec:
  rules:
    - host: the.real.hostname

But the result is the following:

$ kustomize build
apiVersion: extensions/v1beta1
kind: Ingress
metadata:
  annotations:
    kubernetes.io/ingress.class: nginx-external
    nginx.ingress.kubernetes.io/use-regex: "true"
  labels:
    app: asap-ingress-internal
    env: dev
    sia: aza
  name: asap-ingress-internal
  namespace: aza-72461-dev
spec:
  rules:
  - host: the.real.hostname

I have lost all http.paths configuration and I can't find out how to do.

I tried with patches: or patchesStrategicMerge in kustomization.yaml but the result is always the same.

Any help would be greatly appreciated

apiVersion: kustomize.config.k8s.io/v1beta1
kind: Kustomization

resources:
- ../../base/app1

patches:
- target:
    kind: Ingress
    name: my-ingress
  path: ingress-patch.json  

[
    { 
        "op": "replace", 
        "path": "/spec/rules/0/host", 
        "value": "the.real.hostname"
    }
]