Istio ingress gateway and GCP network load balancer

Hi. I am using Istio ingress gateway (istio version 1.18.2), and creating GCP Network (Passthrough) load balancer by using " Internal" annotation in the service.

The load balancer health checks default parameters are Interval 8 seconds, Timeout 1 second, Healthy threshold 1 success, Unhealthy threshold 3 consecutive failures.

When I run load testing, using fortio, and during testing I perform rollout restart for istio ingress gateway deployment, there will be about 20% failures.

If I change the Interval to 4 seconds, in the health checks load balancer parameters, I get a result of 10% errors.

It is also worth noting that changing parameters of istio itself such as
terminationDrainDuration: 30s
have no significant effect on the test result.

So what are the recommendations when using istio ingress gateway and GCP Network load balancer?
And how can I minimize the number of errors during restart of Istio ingress pods?

Thank you,