They are indeed a good progression. My comments are more "compositional": it is not just about getting proportions, in my most humble opinion, it is more important that it "feels right", this depends on the gesture, position and, for portraits, to a very large extent, the direction of the eyes.
For instance, in the upper part of the second picture, the guy with the knife is looking in a different direction than the knife points to. This somehow calls me unnatural, the most natural thing is that if one is going to do something, the eyes go in the direction of the action, one wants to make sure whatever one does is done well, not somewhere else.
Say, when you draw, your eyes focus on the charcoal/pencil, not somewhere else. That's not always true. For example, magicians or a good fighter will looks somewhere else to distract your attention from what they really want to do, but that requires training and not everybody is able to do it (that's why "magic" works).
Shortly put I think you have reached the point where keen observation of the world around you will yield bigger improvements than technique.