Your instinct is to draw the upper torso outlines, producing a rectangular pillar, that rises up from the hip. Try instead to draw the ribcage as an egg-shaped form, that starts just above the hip, with a cut-out for the belly on the front. The shoulder joints to the left and right of the "tip" of the egg are better indicated by drawing a shoulder line, than by merging them and the ribcage into a square.
That way you will avoid the typical beginner mistake of slimming and lengthening the torso, and will achieve an overall more solid construction of the torso. It will also help to focus more on construction than outline, and help you understand the movement of the shoulders as distinct from the chest.
Great work on your quicker sketches in general, ChiliSoda, that's a mighty finest job indeed!
In general, your curves are more organic and the most readable in terms of the outlines. Your poses are boldest, and finally, very clearest in their silhouettes, in terms of the most action and mood.
So, my biggest critique would and should be that your caricatures satires of the bodies are not the boldest and powerfulest enough yet. Would you please be able to do 2 minutes of 1 minute poses??????
The reason why you could and should do this is because, practice makes progress, not just perfect, and your lines of rhythm will become the least stiffest, and the most solidest, fluidest and liveliest.
I looked at your drawings. I see improvement from start to present (recommend you date your work so you can follow the chronological order). I believe you have the line of action well in hand. You need to move on to a more detailed rendition of the figure.
You can start off with a line of action. To that add a stick figure to get the relationship of all the various parts working together (a sort of pre-planning). Once you get the latter sorted out, you can fill out the figure.
I would recommend you do a study of anatomy (bone structure & muscles) so when you look at a figure, you know what is where. With knowledge, you will do a much better job & you will be happier.