im newbie to istio

I need to create custom histogram for a specific metric using annotaion https://istio.io/latest/docs/reference/config/annotations/#SidecarStatsHistogramBuckets , but i cant undertand which prefix would be involved. Istio covers all metrics from itself, but i need 2 specific (say requestresponse size) to have custom histogram and all other default one.

I blindly tried using these https://istio.io/latest/docs/tasks/observability/metrics/customize-metrics/#enable-custom-metrics (REQUEST_,RESPONSE_), using their full name to no effect.