You’ve lost me. Grade thresholds are completely arbitrary. You can peg them at whatever you want, but I don’t see the point in setting an exam that is so difficult that the class median is 40% and then call that an A. In fact forget letter grades completely. Just assign a numeric grade commensurate with the knowledge and it’s application that the student demonstrates relative to the course material. Assignments, tests, and exams should be reflective of the intended learning outcomes for the course. If a student demonstrates high proficiency relative to the course expectations then they should get a grade or mark that reflects that fact. The key here is that the course expectations have to be reasonable. It does not require dumbing down the curriculum or giving points for attendance or completed homework.