The pose is a little strange, it appears has hands are closed and resting somewhat above his hips. A more comfortable version of the pose is to have fingers splayed and on hips rather than above. The arms also seem short. With arms relaxed, elbows are around the bottom of the ribs and wrists are around crotch level. I think there might be something wrong with other body proportions here that's throwing the relationships off.
For the flat pose I'd say it has something to do with his feet being straight together. It's hard to see since you haven't drawn his shoes in yet, but if one leg is in front of the other his hips would be tilted a little and so would his shoulders to compensate.