Those darned ears.  I've overtrimmed my share and had to start with new ones a number of times.  Cutting along the mold line how the ears were trimmed originally may not be the correct line.  A beginner's error is just to trim a fixed amount relative to the outside of the ear for a consistent thickness.  This often results in overtrimming. (The outside of the ear actually plays no part in determining the appropriate trim line except for determining how much ear you have to work with.)  And once