I can't believe what great company I keep here on CA. Your work is really solid. Your life drawings strike me as different from the rest of your studies. Do you use two dimensional reference when you do the rest of your drawings or do you just draw from memory and imagination?
If anything, I think that your life drawings could benefit by sticking to more straight lines and refraining from over-modeling. Basically the figure before you in life drawing is no different than the concepts and ideas you draw from your other studies. Try thinking of it the same way when you are drawing from the model. Also, pay attention to your light source when you are setting up the model pose. You should have a strong direct light with no other indirect light sources complicating the shadows with reflected light from different directions. If you have a clear idea of where the light is coming from, you can almost conceptualize what areas will be hit with light. I think the reclining man in your more recent studies is the best example yet of a definite separation between light and shadow. Try drawing the figure with only black and white tones and describing it as best you can with only those two values, like a poster image. If you start with white paper, block in only the shadow areas. Be careful not to mistake halftone areas for shadow. Make sure to include the whole shadow area, even those areas of reflected light. If you start with a dark toned paper, block in only the light areas, including those for halftone.
For my studies I start out with a the smooth side of a Canson paper, 19 x 24. I pretone the paper with soft charcoal to a medium value. I start out my value studies with blocking in a the shadows with a darker value than the tone of the paper. After this is roughly figured out, I go in and start wiping out the light areas with a chamois. The goal when working in about 4 to 5 values is to put down the medium ones first, reserving your darkest darks and lightest lights for the highlights and accents.
Hope this helps! Oh and they do say that it is important to draw with your whole arm, so standing at the easel helps. Don't know why this is the case though and sometimes my feet get tired.
I wish my conceptual work was up to your level. Please don't hesitate to leave feedback for me at any time. I love your robot studies and characters.
"The progress of learning is from indefinite to definite, not from sensation to perception. We do not learn to have percepts but to differentiate them."