Regarding the Group report VS Graph report.
When comparing the graphs against the group report, you should use "Total"
for the fields which accumulate (total calls, unanswered, total time, etc.)
and always use "Average" for the fields which are averages (average ring
time, duration, average queue time, average agents).
You won't get anything meaningful if you use average of all calls, or total
of average ring time.
Use total of all calls on the graph, and it should match the group report.
Select Total of all calls on the graph side when comparing the two and
they will match. The Graph report shows the agent calls (not ACD calls),
match this against the total calls (not ACD total) on the Group report.