Rule of thumb is as low as possible however like mentioned the ring height is both a personal and equipment based choice. Test to determine if you rings are to high is the same one that you use for setting eye relief. Close your eyes, shoulder your rifle to your natural/familar shooting position and then open your eyes. If you reach or duck to getthe sight pictureyour rings size isn't optimal for your positioning on that rifle. If you have never done this test before you may need to do it a few times to ensure your findings are accurate.