You have two options for dealing with this.
Create a rubric that returns a value between 1 to 16.
Create a rubric which marks from 1-100. Use Moodle Grade Settings to convert this to the PG letter.
Consult the ‘Creating a rubric’ section in this video. Creating a Turnitin Assignment and the basics of marking student papers (VIDEO)
You may also find the guidance on our ‘Assignment Chooser’ page helpful.
Please feel free to consult with your campus learning technologist if you have a query about how to set up your assignments.