Nicely excellent job on your faces and heads, Dorthea. Love the gesture and construction you've got going for them.
Well, if I was to give you a totally honest critique on them, is that most of the heads, although they're very solid on the shapes, lines and spaces, but I really can't help but sense some fearfullness and timidity in the line control and quality. Why don't you please be more cuthroat, bolder, and loosest with the head and expression lines with 14 minutes of 2 minute sketches of those faces and expressions??????????? (7 drawings of heads and expressions of you and models)
The reason?????????? It's because it could and should be able to reduce the rigidity of your shorthands, and to make them cartoony, animated, more vital, and the most energetic. (Hey, at least you'd be able to make more comical and comedic exaggerations of facial anatomy and muscles:D) If this is going to be your newer current goal, then I recommend, allow and encourage you to go ahead with it.
Well, greetings from Salem, MA, USA, and cheers to you!!!