The first head is the actual head of the fashion figure and the last head ends at the ankles.
The first head is the head of the croquis model and the last head is the ankles.
Once you believe you can create a good straight standing croquis illustration, try to practice creating models in different poses (ex. sitting, crouching, standing sideways, etc.)
PRÊT-À-TEMPLATE has croquis models in different paper sizes, model poses, and includes inclusivity (i.e. disabled models, animals, different body shapes).