TaskManagers not scaling in flink Session Deployment using HPA

Question

I've set up a Flink cluster operating in session mode, with Kubernetes underneath. I'm using FlinkK8Operator with helm charts to launch my jobs. I've configured a simple HPA with the deployment, with the below YAML configuration for it. However, the issue is only the job manager pod is scaling, and not task manager pods. Is there a way for me to scale the task manager pods? Additionally, I'm wondering if using HPA for autoscaling the flink session deployment is the right approach?

apiVersion: autoscaling/v2
kind:       HorizontalPodAutoscaler
metadata:
  name: sample-flink-session-hpa
spec:
  scaleTargetRef:
    apiVersion: apps/v1
    kind: Deployment
    name: sample-flink-session-deployment
  minReplicas: 1
  maxReplicas: 10
  metrics:
    - type: Resource
      resource:
        name: cpu
        target:
          type: Utilization
          averageUtilization: 30