Native Dashboard ingestion log_volume (GB) returns no data for scoped (Data RBAC) users, while log_count works

We have Data RBAC configured to segregate visibility between regional SOC teams (per namespace). A scoped analyst group (GRP_SECOPS_SOC-AP) is restricted to namespaces IFAP and UNIFAP via a Data Access Scope using only the standard Namespace label (no custom labels).

IAM bindings on the group (all with the condition resource.name.endsWith("/soc-siem-ap")):

• Chronicle API Restricted Data Access
• Chronicle API Editor
• Chronicle Restricted Data Access Reader (no condition — base UI)
• Custom role with chronicle.nativeDashboards.get/list, chronicle.dashboardCharts.get/list, chronicle.dashboardQueries.get/list

Problem: On a native dashboard panel using the Ingestion metrics data source, the following query returns no data for the scoped analyst, but returns data correctly for a global (unrestricted) admin:

ingestion.component = "Ingestion API"
$namespace = ingestion.namespace
match:
    $namespace
outcome:
    $Total_Log_Volume = math.round(sum(ingestion.log_volume) / (1000 * 1000 * 1000), 4)

If we change the outcome to count(ingestion.log_count), the scoped analyst does see data (correctly filtered to IFAP/UNIFAP). Only the byte/volume metric (sum(ingestion.log_volume)) comes back empty under the scope.

Questions:

1. Is ingestion.log_volume (bandwidth/bytes) expected to not resolve under a Namespace-based Data RBAC scope, while log_count does?
2. If this is by design, what is the supported way to expose approximate ingestion volume (GB) to scoped users in a native dashboard?
3. If not by design, what IAM permission or instance setting enables ingestion volume metrics for scoped users?

Instance region: US.