Hi Dale - Do you have the Project Management setting, "MSP Assignment Units Mapping with PPM Assignment 'Max % Load'" checked? MSP has a tendency to do it's own thing when distributing assignment ETC, but the mapping option allows the project manager to set the Max % Load when assigning resources to tasks in CA PPM. When the schedule is downloaded to MSP and calculated, it is more likely that MSP will respect the assignment units coming from CA PPM. In the scenario you describe, you should also consider using Fixed Units tasks instead of Fixed Duration or Fixed Work, but make sure the project managers have a good understanding of how MSP's scheduling formula handles Fixed Unit tasks vs Fixed Work or Fixed Duration. I hope this information helps.
Katie