Users who have not been granted any permissions/rights which are related to Full License are counted as consuming a full license. This seems to be mostly related to "reporting managers"... we see that all reporting managers are showing as consuming a full license even when those individual resources do not have any permissions granted to them which are associated with a full license.
Release: CODFSS99000-15.3-PPM SAAS FedRAMP-Sandbox-Small Environment
This is due to "Auto-Rights" being assigned to those users when they are made a Resource Manager as it is assumed that Resource Managers will be accessing the application and managing resources, allocations, timesheets etc. for the users for which they are managing as their Resource Manager. This is working as designed.
NOTE: There is a planned feature being added to PPM which will allow for the disabling of auto-rights, such that access rights will not be applied automatically by the system, but rather will need to be manually added by an admin if required. It is not known when the feature will be available as of this time.