How accurately did you depict the overall proportions of the figure?
Not to bad. Small adjustments to arm length needed, bones visible under skin, clavicle in particular need to be more accurately placed. I think only practise can improve this. I still struggle with the rib to pelvis space and getting the brests/abs in the right place on torso. again practise is needed. ankle placement is improving. Not looking so collapsed into heel. Hand, feet and faces I dint even touch on yet so will go back and study these when i get through exercises.
Did you try to imagine the sitters skeletons and muscles?
I did, but I did more anatomical drawings after being disappointed with drawing 3 people exercise. hopefully the next session the skeleton and muscles will be easier to picture as my knowledge has been improved through the anatomical studies I have copied.
Did imagining underlying anatomy help convey structure and form?
Needs to be improve. Chest area i particular can look flat and sunken. Must imagine and sketch in rib cage first. remembering it bows gently towards sternum. Curvature greatly increased on sides, unlike are animal cousins who’s rib cage is shaped in the opposite way to our own.