Hey Tristan, It's important to maintain the gesture of the pose as you move into this stage of adding structure, or your drawings will fall apart. For the most part your proportions are pretty good, but your poses all got very stiff. What I do is start with a gesture drawing, then build the mannequin on top so that I don't loose the gesture. I did a quick sketch to show you what I mean, I hope it helps :)

When I look at these it kind of reminds me of a problem I had not too long ago where I had a very subconscious fear of overlap. I don't have a good method to prescribe for getting rid of it, but I have a hunch that practicing some more base gesture, and slowly integrating those into shapes would prove helpful. Lately I discovered what Ryan Woodward would describe as 'lines of rhythm' in his published sketchbook. The idea is similar to the concept of line of action, except a little less limiting. You're just feeling out the energy and larger rhythms of a pose, and with a charcoal pencil on paper and practicing some pressure control, you can really feel out the sensation of foreshortening as you over lap them in space. I hope that doesn't come off as a terribly b.s response. You just already seem to have the proportion and perspective of these pretty well down so me saying "draw da box bettah" wouldn't feel right lol