By default the grade item's name is shortened to a max of 30 characters. To make it less than 30 you need to edit the grade/report/grader/lib.php file.
608 // Element is a grade_item ... (Lines 609 - 629) 630 . shorten_text($headerlink) . $arrow; Change shorten_text($headerlink) to shorten_text($headerlink, [a number less than 30]) e.g. shorten_text($headerlink, 15)