The distribute Evenly will "Distribute Evenly by Attendee" option only applies if the amount by attendee is enabled, this happens if a company would like to track the dollar amount spent on each attendee individually. This is not commons.
The Distribute Evenly option will distribute the amount of a receipt evenly among the number of attendees. When a group is present, the system will automatically distribute across the total count in the group.
For Example:
If there are 8 6 total attendees, 5 3 attendees in a group and 3 individual attendees, then the amount will be distributed among the 5 6 attendees in the grouptotal.