|Today's model Miranda|
You cannot ask a croquis model to take a posture standing on her toes for more than about 2 minutes. More than 2 minutes must be considered as torture for the croquis model. This sketch is a 2 minutes croquis with some after adjustments.
Mostly you let the croquis model decide which postures she will have but you give a time duration. If that time is more than 2 minutes, the croquis model will take a relaxed posture and if you say 6 minutes or more, then the croquis model takes a lying posture. That's OK. You need to have those croquis exercises, but you also must have postures with "action".
Tell the croquis model to have one minute (or 2 minutes) postures and imaging being an athlet and you will get a series of some good balance exercises for your croquis session.