Help with a report comparing actuals against target

Example Scenario:
20 Users each with a sales target (stored in users_cstm.target_c)
5 Departments each with 4 users (stored in users.department)
Each Account has a value (stored in accounts_cstm.billed_c)
Each User is Assigned To Accounts

Required Report: Monitor the performance of each department. Billed Amount against Target

We have tried the following
Primary Module: Accounts
Group by Accounts>Assigned to user>Department
Sum Accounts>Assigned to user> Target
Sum Accounts>Billed

Cant seem to get it to work.
Target summation does add up correctly.

We’ve tried setting Primary module to Users but there is no link to Accounts from there.

Is this possible?

We have found a workaround using a union.