Hi Dr. A:
I think one approach to setting up a grading system is to examine the Student Learning Outcomes (SLO's), course objectives, and program description. Using a variety of assessment instruments to grade against the SLO's improves the chances the student demonstrate their knowledge.
Finding the right mix is a challenge, is never easy (requires trial and error), and requires a committed and caring instructor to continuously try to discover the best balance. Good Luck!
Regards, Barry