Support/Customer Services Reporting: Average Time metrics

The native NetSuite support metrics are great when reporting on support cases by employee/rep.  The ones I'm talking about are:

[LIST]
[*]Avg. Initial Response Time
[*]Avg. Time To Assign
[*]First Contact Resolution Rate
[*]Avg. Interactions
[*]Avg Time To Close
[/LIST]

However these seem to only be tracked at the employee level, without any ability to report on them at a summary level, by native or custom categories (e.g. "area", "product", "issue").  Is this indeed a limitation or am I missing a way of doing this?

I've tried creating a custom report, grouping by "Area" (a custom field on support cases), and even if I remove "Support Rep" from the results, there's still a line in the report for every rep, a no summary results when you collapse columns.