Here is an example of a woman with a short crop and this picture shows the process of working in sections to straighten.
This is a side view which shows how the back is cut into a stacked shape where the inside layers are longer and they gradually get shorter working toward the outer layer. This creates sleek lines that accentuate the neck and shapely feminine curves. When a super straight look is desired, sectioning off the strands helps to work with small pieces making it easier to get the results.