We want staff to get the email reports just from the groups they oversee.

Under the groups button are coach and staff areas. These were designed to do exactly what you want. Add in the people who oversee groups as coaches, then assign the groups underneath them. They will get the emails just from these groups. If you have another level above that, then use the staff area and assign coaches to the staff. Staff also get the emails of all groups underneath their coaches.

Then, on Basic Settings, step #1 remove the email addresses from receiving attendance reports. All emails listed there will get all attendance reports no matter what.

Basic settings, step #1 also allows you to customize the names you give to leaders, coaches and area leaders (staff).