Which is hilarious, since Helena is 5'11", and Cass is 5'6" or something.
Also, Steph "failed" because Batman set her up for failure. Instead of giving her his trust, and training her for the type of decision making she would need for the kind of circumstances that led to her disobedience, Batman screwed with her head by giving her a partial trust (not telling her crucial information like Matches Malones, and possibly never even telling her that he was Bruce Wayne, since he keeps the cowl on during her training montage), but a completely arbitrary and vague "You can never disobey me or you're fired" red line.